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* [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu
@ 2025-04-09 21:11 Ingo Molnar
  2025-04-09 21:11 ` [PATCH 1/8] x86/fpu: Introduce the x86_task_fpu() helper method Ingo Molnar
                   ` (15 more replies)
  0 siblings, 16 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar

This series is one of the dependencies of the fast-headers work,
which aims to reduce header complexity by removing <asm/processor.h>
from the <linux/sched.h> dependency chain, which headers are headers
are fat enough already even if we do not combine them.

To achieve that decoupling, one of the key steps is to not embedd any
C types from <asm/processor.h> into task_struct.

The only architecture that relies on that in a serious fashion is x86,
via the 'struct thread::fpu' variable size structure. The series below
attempts to resolve it by using a calculated fpu context area address
value via the x86_task_fpu() helper. The allocation layout of
task_struct + fpu-save-area doesn't change.

The -v5 version is a refresh of the -v4 series to v6.15-rc1.

The Git tree of these commits can also be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/mingo/tip.git WIP.x86/fpu

Thanks,

	Ingo

===============>
Ingo Molnar (8):
  x86/fpu: Introduce the x86_task_fpu() helper method
  x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu()
  x86/fpu: Make task_struct::thread constant size
  x86/fpu: Remove the thread::fpu pointer
  x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call
  x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit
  x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks
  x86/fpu: Use 'fpstate' variable names consistently

 arch/x86/include/asm/fpu/api.h   |  2 +-
 arch/x86/include/asm/fpu/sched.h |  4 +-
 arch/x86/include/asm/processor.h | 23 ++++++------
 arch/x86/kernel/fpu/context.h    |  4 +-
 arch/x86/kernel/fpu/core.c       | 80 +++++++++++++++++++++++-----------------
 arch/x86/kernel/fpu/init.c       | 21 ++++++-----
 arch/x86/kernel/fpu/regset.c     | 22 +++++------
 arch/x86/kernel/fpu/signal.c     | 18 ++++-----
 arch/x86/kernel/fpu/xstate.c     | 27 ++++++--------
 arch/x86/kernel/fpu/xstate.h     |  6 +--
 arch/x86/kernel/process.c        |  9 ++---
 arch/x86/kernel/signal.c         |  6 +--
 arch/x86/kernel/traps.c          |  2 +-
 arch/x86/math-emu/fpu_aux.c      |  2 +-
 arch/x86/math-emu/fpu_entry.c    |  4 +-
 arch/x86/math-emu/fpu_system.h   |  2 +-
 arch/x86/mm/extable.c            |  2 +-
 include/linux/sched.h            | 15 ++------
 18 files changed, 126 insertions(+), 123 deletions(-)

-- 
2.45.2


^ permalink raw reply	[flat|nested] 43+ messages in thread
* [PATCH 1/8] x86/fpu: Introduce the x86_task_fpu() helper method
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-09 21:11 ` [PATCH 2/8] x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu() Ingo Molnar
                   ` (14 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar

The per-task FPU context/save area is allocated right
next to task_struct, currently in a variable-size
array via task_struct::thread.fpu[], but we plan to
fully hide it from the C type scope.

Introduce the x86_task_fpu() accessor that gets to the
FPU context pointer explicitly from the task pointer.

Right now this is a simple (task)->thread.fpu wrapper.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/processor.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 5d2f7e5aff26..2f631e0adea3 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -523,6 +523,8 @@ struct thread_struct {
 	 */
 };
 
+#define x86_task_fpu(task) (&(task)->thread.fpu)
+
 extern void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size);
 
 static inline void arch_thread_struct_whitelist(unsigned long *offset,
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH 2/8] x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu()
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
  2025-04-09 21:11 ` [PATCH 1/8] x86/fpu: Introduce the x86_task_fpu() helper method Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-09 21:11 ` [PATCH 3/8] x86/fpu: Make task_struct::thread constant size Ingo Molnar
                   ` (13 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar

This will make the removal of the task_struct::thread.fpu array
easier.

No change in functionality - code generated before and after this
commit is identical on x86-defconfig:

  kepler:~/tip> diff -up vmlinux.before.asm vmlinux.after.asm
  kepler:~/tip>

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/fpu/sched.h |  2 +-
 arch/x86/kernel/fpu/context.h    |  4 ++--
 arch/x86/kernel/fpu/core.c       | 30 +++++++++++++++---------------
 arch/x86/kernel/fpu/init.c       |  8 ++++----
 arch/x86/kernel/fpu/regset.c     | 22 +++++++++++-----------
 arch/x86/kernel/fpu/signal.c     | 18 +++++++++---------
 arch/x86/kernel/fpu/xstate.c     | 22 +++++++++++-----------
 arch/x86/kernel/fpu/xstate.h     |  6 +++---
 arch/x86/kernel/process.c        |  6 +++---
 arch/x86/kernel/signal.c         |  6 +++---
 arch/x86/kernel/traps.c          |  2 +-
 arch/x86/math-emu/fpu_aux.c      |  2 +-
 arch/x86/math-emu/fpu_entry.c    |  4 ++--
 arch/x86/math-emu/fpu_system.h   |  2 +-
 arch/x86/mm/extable.c            |  2 +-
 15 files changed, 68 insertions(+), 68 deletions(-)

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index c485f1944c5f..1feaa68b7567 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -41,7 +41,7 @@ static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
 {
 	if (cpu_feature_enabled(X86_FEATURE_FPU) &&
 	    !(old->flags & (PF_KTHREAD | PF_USER_WORKER))) {
-		struct fpu *old_fpu = &old->thread.fpu;
+		struct fpu *old_fpu = x86_task_fpu(old);
 
 		save_fpregs_to_fpstate(old_fpu);
 		/*
diff --git a/arch/x86/kernel/fpu/context.h b/arch/x86/kernel/fpu/context.h
index f6d856bd50bc..10d0a720659c 100644
--- a/arch/x86/kernel/fpu/context.h
+++ b/arch/x86/kernel/fpu/context.h
@@ -53,7 +53,7 @@ static inline void fpregs_activate(struct fpu *fpu)
 /* Internal helper for switch_fpu_return() and signal frame setup */
 static inline void fpregs_restore_userregs(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	int cpu = smp_processor_id();
 
 	if (WARN_ON_ONCE(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
@@ -67,7 +67,7 @@ static inline void fpregs_restore_userregs(void)
 		 * If PKRU is enabled, then the PKRU value is already
 		 * correct because it was either set in switch_to() or in
 		 * flush_thread(). So it is excluded because it might be
-		 * not up to date in current->thread.fpu.xsave state.
+		 * not up to date in current->thread.fpu->xsave state.
 		 *
 		 * XFD state is handled in restore_fpregs_from_fpstate().
 		 */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 91d6341f281f..dc6d7f93c446 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -211,7 +211,7 @@ static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 		return;
 
 	spin_lock_irq(&current->sighand->siglock);
-	fpuperm = &current->group_leader->thread.fpu.guest_perm;
+	fpuperm = &x86_task_fpu(current->group_leader)->guest_perm;
 	perm = fpuperm->__state_perm;
 
 	/* First fpstate allocation locks down permissions. */
@@ -323,7 +323,7 @@ EXPORT_SYMBOL_GPL(fpu_update_guest_xfd);
  */
 void fpu_sync_guest_vmexit_xfd_state(void)
 {
-	struct fpstate *fps = current->thread.fpu.fpstate;
+	struct fpstate *fps = x86_task_fpu(current)->fpstate;
 
 	lockdep_assert_irqs_disabled();
 	if (fpu_state_size_dynamic()) {
@@ -337,7 +337,7 @@ EXPORT_SYMBOL_GPL(fpu_sync_guest_vmexit_xfd_state);
 int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
 {
 	struct fpstate *guest_fps = guest_fpu->fpstate;
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	struct fpstate *cur_fps = fpu->fpstate;
 
 	fpregs_lock();
@@ -438,7 +438,7 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 	if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER)) &&
 	    !test_thread_flag(TIF_NEED_FPU_LOAD)) {
 		set_thread_flag(TIF_NEED_FPU_LOAD);
-		save_fpregs_to_fpstate(&current->thread.fpu);
+		save_fpregs_to_fpstate(x86_task_fpu(current));
 	}
 	__cpu_invalidate_fpregs_state();
 
@@ -467,7 +467,7 @@ EXPORT_SYMBOL_GPL(kernel_fpu_end);
  */
 void fpu_sync_fpstate(struct fpu *fpu)
 {
-	WARN_ON_FPU(fpu != &current->thread.fpu);
+	WARN_ON_FPU(fpu != x86_task_fpu(current));
 
 	fpregs_lock();
 	trace_x86_fpu_before_save(fpu);
@@ -552,7 +552,7 @@ void fpstate_reset(struct fpu *fpu)
 static inline void fpu_inherit_perms(struct fpu *dst_fpu)
 {
 	if (fpu_state_size_dynamic()) {
-		struct fpu *src_fpu = &current->group_leader->thread.fpu;
+		struct fpu *src_fpu = x86_task_fpu(current->group_leader);
 
 		spin_lock_irq(&current->sighand->siglock);
 		/* Fork also inherits the permissions of the parent */
@@ -572,7 +572,7 @@ static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp)
 	if (!ssp)
 		return 0;
 
-	xstate = get_xsave_addr(&dst->thread.fpu.fpstate->regs.xsave,
+	xstate = get_xsave_addr(&x86_task_fpu(dst)->fpstate->regs.xsave,
 				XFEATURE_CET_USER);
 
 	/*
@@ -593,8 +593,8 @@ static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp)
 int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	      unsigned long ssp)
 {
-	struct fpu *src_fpu = &current->thread.fpu;
-	struct fpu *dst_fpu = &dst->thread.fpu;
+	struct fpu *src_fpu = x86_task_fpu(current);
+	struct fpu *dst_fpu = x86_task_fpu(dst);
 
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
@@ -686,7 +686,7 @@ void fpu__drop(struct fpu *fpu)
 {
 	preempt_disable();
 
-	if (fpu == &current->thread.fpu) {
+	if (fpu == x86_task_fpu(current)) {
 		/* Ignore delayed exceptions from user space */
 		asm volatile("1: fwait\n"
 			     "2:\n"
@@ -720,7 +720,7 @@ static inline void restore_fpregs_from_init_fpstate(u64 features_mask)
  */
 static void fpu_reset_fpregs(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	fpregs_lock();
 	__fpu_invalidate_fpregs_state(fpu);
@@ -749,7 +749,7 @@ static void fpu_reset_fpregs(void)
  */
 void fpu__clear_user_states(struct fpu *fpu)
 {
-	WARN_ON_FPU(fpu != &current->thread.fpu);
+	WARN_ON_FPU(fpu != x86_task_fpu(current));
 
 	fpregs_lock();
 	if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
@@ -782,7 +782,7 @@ void fpu__clear_user_states(struct fpu *fpu)
 
 void fpu_flush_thread(void)
 {
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 	fpu_reset_fpregs();
 }
 /*
@@ -823,7 +823,7 @@ void fpregs_lock_and_load(void)
  */
 void fpregs_assert_state_consistent(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		return;
@@ -835,7 +835,7 @@ EXPORT_SYMBOL_GPL(fpregs_assert_state_consistent);
 
 void fpregs_mark_activate(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	fpregs_activate(fpu);
 	fpu->last_cpu = smp_processor_id();
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 998a08f17e33..ad5cb2943d37 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -38,7 +38,7 @@ static void fpu__init_cpu_generic(void)
 	/* Flush out any pending x87 state: */
 #ifdef CONFIG_MATH_EMULATION
 	if (!boot_cpu_has(X86_FEATURE_FPU))
-		fpstate_init_soft(&current->thread.fpu.fpstate->regs.soft);
+		fpstate_init_soft(&x86_task_fpu(current)->fpstate->regs.soft);
 	else
 #endif
 		asm volatile ("fninit");
@@ -154,7 +154,7 @@ static void __init fpu__init_task_struct_size(void)
 	 * Subtract off the static size of the register state.
 	 * It potentially has a bunch of padding.
 	 */
-	task_size -= sizeof(current->thread.fpu.__fpstate.regs);
+	task_size -= sizeof(union fpregs_state);
 
 	/*
 	 * Add back the dynamically-calculated register state
@@ -204,7 +204,7 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	fpu_kernel_cfg.default_size = size;
 	fpu_user_cfg.max_size = size;
 	fpu_user_cfg.default_size = size;
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 }
 
 /*
@@ -213,7 +213,7 @@ static void __init fpu__init_system_xstate_size_legacy(void)
  */
 void __init fpu__init_system(void)
 {
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 	fpu__init_system_early_generic();
 
 	/*
diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 887b0b8e21e3..0986c2200adc 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -45,7 +45,7 @@ int regset_xregset_fpregs_active(struct task_struct *target, const struct user_r
  */
 static void sync_fpstate(struct fpu *fpu)
 {
-	if (fpu == &current->thread.fpu)
+	if (fpu == x86_task_fpu(current))
 		fpu_sync_fpstate(fpu);
 }
 
@@ -63,7 +63,7 @@ static void fpu_force_restore(struct fpu *fpu)
 	 * Only stopped child tasks can be used to modify the FPU
 	 * state in the fpstate buffer:
 	 */
-	WARN_ON_FPU(fpu == &current->thread.fpu);
+	WARN_ON_FPU(fpu == x86_task_fpu(current));
 
 	__fpu_invalidate_fpregs_state(fpu);
 }
@@ -71,7 +71,7 @@ static void fpu_force_restore(struct fpu *fpu)
 int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
 		struct membuf to)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 
 	if (!cpu_feature_enabled(X86_FEATURE_FXSR))
 		return -ENODEV;
@@ -91,7 +91,7 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 		unsigned int pos, unsigned int count,
 		const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct fxregs_state newstate;
 	int ret;
 
@@ -133,7 +133,7 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
 	if (!cpu_feature_enabled(X86_FEATURE_XSAVE))
 		return -ENODEV;
 
-	sync_fpstate(&target->thread.fpu);
+	sync_fpstate(x86_task_fpu(target));
 
 	copy_xstate_to_uabi_buf(to, target, XSTATE_COPY_XSAVE);
 	return 0;
@@ -143,7 +143,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
 		  unsigned int pos, unsigned int count,
 		  const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct xregs_state *tmpbuf = NULL;
 	int ret;
 
@@ -187,7 +187,7 @@ int ssp_active(struct task_struct *target, const struct user_regset *regset)
 int ssp_get(struct task_struct *target, const struct user_regset *regset,
 	    struct membuf to)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct cet_user_state *cetregs;
 
 	if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) ||
@@ -214,7 +214,7 @@ int ssp_set(struct task_struct *target, const struct user_regset *regset,
 	    unsigned int pos, unsigned int count,
 	    const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct xregs_state *xsave = &fpu->fpstate->regs.xsave;
 	struct cet_user_state *cetregs;
 	unsigned long user_ssp;
@@ -368,7 +368,7 @@ static void __convert_from_fxsr(struct user_i387_ia32_struct *env,
 void
 convert_from_fxsr(struct user_i387_ia32_struct *env, struct task_struct *tsk)
 {
-	__convert_from_fxsr(env, tsk, &tsk->thread.fpu.fpstate->regs.fxsave);
+	__convert_from_fxsr(env, tsk, &x86_task_fpu(tsk)->fpstate->regs.fxsave);
 }
 
 void convert_to_fxsr(struct fxregs_state *fxsave,
@@ -401,7 +401,7 @@ void convert_to_fxsr(struct fxregs_state *fxsave,
 int fpregs_get(struct task_struct *target, const struct user_regset *regset,
 	       struct membuf to)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct user_i387_ia32_struct env;
 	struct fxregs_state fxsave, *fx;
 
@@ -433,7 +433,7 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 	       unsigned int pos, unsigned int count,
 	       const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct user_i387_ia32_struct env;
 	int ret;
 
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 6c69cb28b298..b8b4fa9c2d04 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -43,13 +43,13 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
 	 * fpstate layout with out copying the extended state information
 	 * in the memory layout.
 	 */
-	if (__get_user(magic2, (__u32 __user *)(fpstate + current->thread.fpu.fpstate->user_size)))
+	if (__get_user(magic2, (__u32 __user *)(fpstate + x86_task_fpu(current)->fpstate->user_size)))
 		return false;
 
 	if (likely(magic2 == FP_XSTATE_MAGIC2))
 		return true;
 setfx:
-	trace_x86_fpu_xstate_check_failed(&current->thread.fpu);
+	trace_x86_fpu_xstate_check_failed(x86_task_fpu(current));
 
 	/* Set the parameters for fx only state */
 	fx_sw->magic1 = 0;
@@ -64,13 +64,13 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
 static inline bool save_fsave_header(struct task_struct *tsk, void __user *buf)
 {
 	if (use_fxsr()) {
-		struct xregs_state *xsave = &tsk->thread.fpu.fpstate->regs.xsave;
+		struct xregs_state *xsave = &x86_task_fpu(tsk)->fpstate->regs.xsave;
 		struct user_i387_ia32_struct env;
 		struct _fpstate_32 __user *fp = buf;
 
 		fpregs_lock();
 		if (!test_thread_flag(TIF_NEED_FPU_LOAD))
-			fxsave(&tsk->thread.fpu.fpstate->regs.fxsave);
+			fxsave(&x86_task_fpu(tsk)->fpstate->regs.fxsave);
 		fpregs_unlock();
 
 		convert_from_fxsr(&env, tsk);
@@ -184,7 +184,7 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf, u32 pk
 bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size, u32 pkru)
 {
 	struct task_struct *tsk = current;
-	struct fpstate *fpstate = tsk->thread.fpu.fpstate;
+	struct fpstate *fpstate = x86_task_fpu(tsk)->fpstate;
 	bool ia32_fxstate = (buf != buf_fx);
 	int ret;
 
@@ -272,7 +272,7 @@ static int __restore_fpregs_from_user(void __user *buf, u64 ufeatures,
  */
 static bool restore_fpregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	int ret;
 
 	/* Restore enabled features only. */
@@ -332,7 +332,7 @@ static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
 			      bool ia32_fxstate)
 {
 	struct task_struct *tsk = current;
-	struct fpu *fpu = &tsk->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(tsk);
 	struct user_i387_ia32_struct env;
 	bool success, fx_only = false;
 	union fpregs_state *fpregs;
@@ -452,7 +452,7 @@ static inline unsigned int xstate_sigframe_size(struct fpstate *fpstate)
  */
 bool fpu__restore_sig(void __user *buf, int ia32_frame)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	void __user *buf_fx = buf;
 	bool ia32_fxstate = false;
 	bool success = false;
@@ -499,7 +499,7 @@ unsigned long
 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 		     unsigned long *buf_fx, unsigned long *size)
 {
-	unsigned long frame_size = xstate_sigframe_size(current->thread.fpu.fpstate);
+	unsigned long frame_size = xstate_sigframe_size(x86_task_fpu(current)->fpstate);
 
 	*buf_fx = sp = round_down(sp - frame_size, 64);
 	if (ia32_frame && use_fxsr()) {
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 6a41d1610d8b..ab2588b8f17f 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -727,7 +727,7 @@ static void __init fpu__init_disable_system_xstate(unsigned int legacy_size)
 	 */
 	init_fpstate.xfd = 0;
 
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 }
 
 /*
@@ -835,7 +835,7 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
 		goto out_disable;
 
 	/* Reset the state for the current task */
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 
 	/*
 	 * Update info used for ptrace frames; use standard-format size and no
@@ -909,7 +909,7 @@ void fpu__resume_cpu(void)
 	}
 
 	if (fpu_state_size_dynamic())
-		wrmsrl(MSR_IA32_XFD, current->thread.fpu.fpstate->xfd);
+		wrmsrl(MSR_IA32_XFD, x86_task_fpu(current)->fpstate->xfd);
 }
 
 /*
@@ -1191,8 +1191,8 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
 void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
 			     enum xstate_copy_mode copy_mode)
 {
-	__copy_xstate_to_uabi_buf(to, tsk->thread.fpu.fpstate,
-				  tsk->thread.fpu.fpstate->user_xfeatures,
+	__copy_xstate_to_uabi_buf(to, x86_task_fpu(tsk)->fpstate,
+				  x86_task_fpu(tsk)->fpstate->user_xfeatures,
 				  tsk->thread.pkru, copy_mode);
 }
 
@@ -1332,7 +1332,7 @@ int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u
 int copy_sigframe_from_user_to_xstate(struct task_struct *tsk,
 				      const void __user *ubuf)
 {
-	return copy_uabi_to_xstate(tsk->thread.fpu.fpstate, NULL, ubuf, &tsk->thread.pkru);
+	return copy_uabi_to_xstate(x86_task_fpu(tsk)->fpstate, NULL, ubuf, &tsk->thread.pkru);
 }
 
 static bool validate_independent_components(u64 mask)
@@ -1426,7 +1426,7 @@ static bool xstate_op_valid(struct fpstate *fpstate, u64 mask, bool rstor)
 	  * The XFD MSR does not match fpstate->xfd. That's invalid when
 	  * the passed in fpstate is current's fpstate.
 	  */
-	if (fpstate->xfd == current->thread.fpu.fpstate->xfd)
+	if (fpstate->xfd == x86_task_fpu(current)->fpstate->xfd)
 		return false;
 
 	/*
@@ -1503,7 +1503,7 @@ void fpstate_free(struct fpu *fpu)
 static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
 			   unsigned int usize, struct fpu_guest *guest_fpu)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	struct fpstate *curfps, *newfps = NULL;
 	unsigned int fpsize;
 	bool in_use;
@@ -1596,7 +1596,7 @@ static int __xstate_request_perm(u64 permitted, u64 requested, bool guest)
 	 * AVX512.
 	 */
 	bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
-	struct fpu *fpu = &current->group_leader->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current->group_leader);
 	struct fpu_state_perm *perm;
 	unsigned int ksize, usize;
 	u64 mask;
@@ -1699,7 +1699,7 @@ int __xfd_enable_feature(u64 xfd_err, struct fpu_guest *guest_fpu)
 		return -EPERM;
 	}
 
-	fpu = &current->group_leader->thread.fpu;
+	fpu = x86_task_fpu(current->group_leader);
 	perm = guest_fpu ? &fpu->guest_perm : &fpu->perm;
 	ksize = perm->__state_size;
 	usize = perm->__user_state_size;
@@ -1804,7 +1804,7 @@ long fpu_xstate_prctl(int option, unsigned long arg2)
  */
 static void avx512_status(struct seq_file *m, struct task_struct *task)
 {
-	unsigned long timestamp = READ_ONCE(task->thread.fpu.avx512_timestamp);
+	unsigned long timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp);
 	long delta;
 
 	if (!timestamp) {
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 0fd34f53f025..9a3a8ccf13bf 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -22,7 +22,7 @@ static inline void xstate_init_xcomp_bv(struct xregs_state *xsave, u64 mask)
 
 static inline u64 xstate_get_group_perm(bool guest)
 {
-	struct fpu *fpu = &current->group_leader->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current->group_leader);
 	struct fpu_state_perm *perm;
 
 	/* Pairs with WRITE_ONCE() in xstate_request_perm() */
@@ -288,7 +288,7 @@ static inline int xsave_to_user_sigframe(struct xregs_state __user *buf, u32 pkr
 	 * internally, e.g. PKRU. That's user space ABI and also required
 	 * to allow the signal handler to modify PKRU.
 	 */
-	struct fpstate *fpstate = current->thread.fpu.fpstate;
+	struct fpstate *fpstate = x86_task_fpu(current)->fpstate;
 	u64 mask = fpstate->user_xfeatures;
 	u32 lmask;
 	u32 hmask;
@@ -322,7 +322,7 @@ static inline int xrstor_from_user_sigframe(struct xregs_state __user *buf, u64
 	u32 hmask = mask >> 32;
 	int err;
 
-	xfd_validate_state(current->thread.fpu.fpstate, mask, true);
+	xfd_validate_state(x86_task_fpu(current)->fpstate, mask, true);
 
 	stac();
 	XSTATE_OP(XRSTOR, xstate, lmask, hmask, err);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 962c3ce39323..47694e391506 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -103,7 +103,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 	dst->thread.vm86 = NULL;
 #endif
 	/* Drop the copied pointer to current's fpstate */
-	dst->thread.fpu.fpstate = NULL;
+	x86_task_fpu(dst)->fpstate = NULL;
 
 	return 0;
 }
@@ -112,7 +112,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 void arch_release_task_struct(struct task_struct *tsk)
 {
 	if (fpu_state_size_dynamic())
-		fpstate_free(&tsk->thread.fpu);
+		fpstate_free(x86_task_fpu(tsk));
 }
 #endif
 
@@ -122,7 +122,7 @@ void arch_release_task_struct(struct task_struct *tsk)
 void exit_thread(struct task_struct *tsk)
 {
 	struct thread_struct *t = &tsk->thread;
-	struct fpu *fpu = &t->fpu;
+	struct fpu *fpu = x86_task_fpu(tsk);
 
 	if (test_thread_flag(TIF_IO_BITMAP))
 		io_bitmap_exit(tsk);
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 5f441039b572..2404233336ab 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -255,7 +255,7 @@ static void
 handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 {
 	bool stepping, failed;
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	if (v8086_mode(regs))
 		save_v86_state((struct kernel_vm86_regs *) regs, VM86_SIGNAL);
@@ -423,14 +423,14 @@ bool sigaltstack_size_valid(size_t ss_size)
 	if (!fpu_state_size_dynamic() && !strict_sigaltstack_size)
 		return true;
 
-	fsize += current->group_leader->thread.fpu.perm.__user_state_size;
+	fsize += x86_task_fpu(current->group_leader)->perm.__user_state_size;
 	if (likely(ss_size > fsize))
 		return true;
 
 	if (strict_sigaltstack_size)
 		return ss_size > fsize;
 
-	mask = current->group_leader->thread.fpu.perm.__state_perm;
+	mask = x86_task_fpu(current->group_leader)->perm.__state_perm;
 	if (mask & XFEATURE_MASK_USER_DYNAMIC)
 		return ss_size > fsize;
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 9f88b8a78e50..f48325dfaa01 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1295,7 +1295,7 @@ DEFINE_IDTENTRY_RAW(exc_debug)
 static void math_error(struct pt_regs *regs, int trapnr)
 {
 	struct task_struct *task = current;
-	struct fpu *fpu = &task->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(task);
 	int si_code;
 	char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
 						"simd exception";
diff --git a/arch/x86/math-emu/fpu_aux.c b/arch/x86/math-emu/fpu_aux.c
index d62662bdd460..5f253ae406b6 100644
--- a/arch/x86/math-emu/fpu_aux.c
+++ b/arch/x86/math-emu/fpu_aux.c
@@ -53,7 +53,7 @@ void fpstate_init_soft(struct swregs_state *soft)
 
 void finit(void)
 {
-	fpstate_init_soft(&current->thread.fpu.fpstate->regs.soft);
+	fpstate_init_soft(&x86_task_fpu(current)->fpstate->regs.soft);
 }
 
 /*
diff --git a/arch/x86/math-emu/fpu_entry.c b/arch/x86/math-emu/fpu_entry.c
index 91c52ead1226..5034df617740 100644
--- a/arch/x86/math-emu/fpu_entry.c
+++ b/arch/x86/math-emu/fpu_entry.c
@@ -641,7 +641,7 @@ int fpregs_soft_set(struct task_struct *target,
 		    unsigned int pos, unsigned int count,
 		    const void *kbuf, const void __user *ubuf)
 {
-	struct swregs_state *s387 = &target->thread.fpu.fpstate->regs.soft;
+	struct swregs_state *s387 = &x86_task_fpu(target)->fpstate->regs.soft;
 	void *space = s387->st_space;
 	int ret;
 	int offset, other, i, tags, regnr, tag, newtop;
@@ -692,7 +692,7 @@ int fpregs_soft_get(struct task_struct *target,
 		    const struct user_regset *regset,
 		    struct membuf to)
 {
-	struct swregs_state *s387 = &target->thread.fpu.fpstate->regs.soft;
+	struct swregs_state *s387 = &x86_task_fpu(target)->fpstate->regs.soft;
 	const void *space = s387->st_space;
 	int offset = (S387->ftop & 7) * 10, other = 80 - offset;
 
diff --git a/arch/x86/math-emu/fpu_system.h b/arch/x86/math-emu/fpu_system.h
index eec3e4805c75..5e238e930fe3 100644
--- a/arch/x86/math-emu/fpu_system.h
+++ b/arch/x86/math-emu/fpu_system.h
@@ -73,7 +73,7 @@ static inline bool seg_writable(struct desc_struct *d)
 	return (d->type & SEG_TYPE_EXECUTE_MASK) == SEG_TYPE_WRITABLE;
 }
 
-#define I387			(&current->thread.fpu.fpstate->regs)
+#define I387			(&x86_task_fpu(current)->fpstate->regs)
 #define FPU_info		(I387->soft.info)
 
 #define FPU_CS			(*(unsigned short *) &(FPU_info->regs->cs))
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 51986e8a9d35..bf8dab18be97 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -111,7 +111,7 @@ static bool ex_handler_sgx(const struct exception_table_entry *fixup,
 
 /*
  * Handler for when we fail to restore a task's FPU state.  We should never get
- * here because the FPU state of a task using the FPU (task->thread.fpu.state)
+ * here because the FPU state of a task using the FPU (struct fpu::fpstate)
  * should always be valid.  However, past bugs have allowed userspace to set
  * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn().
  * These caused XRSTOR to fail when switching to the task, leaking the FPU
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH 3/8] x86/fpu: Make task_struct::thread constant size
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
  2025-04-09 21:11 ` [PATCH 1/8] x86/fpu: Introduce the x86_task_fpu() helper method Ingo Molnar
  2025-04-09 21:11 ` [PATCH 2/8] x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu() Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-09 21:11 ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
                   ` (12 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar, Andy Lutomirski,
	Fenghua Yu, Dave Hansen, Uros Bizjak

Turn thread.fpu into a pointer. Since most FPU code internals work by passing
around the FPU pointer already, the code generation impact is small.

This allows us to remove the old kludge of task_struct being variable size:

  struct task_struct {

       ...
       /*
        * New fields for task_struct should be added above here, so that
        * they are included in the randomized portion of task_struct.
        */
       randomized_struct_fields_end

       /* CPU-specific state of this task: */
       struct thread_struct            thread;

       /*
        * WARNING: on x86, 'thread_struct' contains a variable-sized
        * structure.  It *MUST* be at the end of 'task_struct'.
        *
        * Do not put anything below here!
        */
  };

... which creates a number of problems, such as requiring thread_struct to be
the last member of the struct - not allowing it to be struct-randomized, etc.

But the primary motivation is to allow the decoupling of task_struct from
hardware details (<asm/processor.h> in particular), and to eventually allow
the per-task infrastructure:

   DECLARE_PER_TASK(type, name);
   ...
   per_task(current, name) = val;

... which requires task_struct to be a constant size struct.

The fpu_thread_struct_whitelist() quirk to hardened usercopy can be removed,
now that the FPU structure is not embedded in the task struct anymore, which
reduces text footprint a bit.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fixed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20240605083557.2051480-2-mingo@kernel.org
---
 arch/x86/include/asm/processor.h | 20 +++++++++-----------
 arch/x86/kernel/fpu/core.c       | 23 ++++++++++++-----------
 arch/x86/kernel/fpu/init.c       | 17 ++++++++++-------
 arch/x86/kernel/process.c        |  2 +-
 include/linux/sched.h            | 15 ++++-----------
 5 files changed, 36 insertions(+), 41 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 2f631e0adea3..5ea7e5d2c4de 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -516,21 +516,19 @@ struct thread_struct {
 #endif
 
 	/* Floating point and extended processor state */
-	struct fpu		fpu;
-	/*
-	 * WARNING: 'fpu' is dynamically-sized.  It *MUST* be at
-	 * the end.
-	 */
+	struct fpu		*fpu;
 };
 
-#define x86_task_fpu(task) (&(task)->thread.fpu)
-
-extern void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size);
+#define x86_task_fpu(task) ((task)->thread.fpu)
 
-static inline void arch_thread_struct_whitelist(unsigned long *offset,
-						unsigned long *size)
+/*
+ * X86 doesn't need any embedded-FPU-struct quirks:
+ */
+static inline void
+arch_thread_struct_whitelist(unsigned long *offset, unsigned long *size)
 {
-	fpu_thread_struct_whitelist(offset, size);
+	*offset = 0;
+	*size = 0;
 }
 
 static inline void
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index dc6d7f93c446..853a738fdf2d 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -593,8 +593,19 @@ static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp)
 int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	      unsigned long ssp)
 {
+	/*
+	 * We allocate the new FPU structure right after the end of the task struct.
+	 * task allocation size already took this into account.
+	 *
+	 * This is safe because task_struct size is a multiple of cacheline size.
+	 */
 	struct fpu *src_fpu = x86_task_fpu(current);
-	struct fpu *dst_fpu = x86_task_fpu(dst);
+	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
+
+	BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
+	BUG_ON(!src_fpu);
+
+	dst->thread.fpu = dst_fpu;
 
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
@@ -663,16 +674,6 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	return 0;
 }
 
-/*
- * Whitelist the FPU register state embedded into task_struct for hardened
- * usercopy.
- */
-void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size)
-{
-	*offset = offsetof(struct thread_struct, fpu.__fpstate.regs);
-	*size = fpu_kernel_cfg.default_size;
-}
-
 /*
  * Drops current FPU state: deactivates the fpregs and
  * the fpstate. NOTE: it still leaves previous contents
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index ad5cb2943d37..848ea79886ba 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -71,8 +71,15 @@ static bool __init fpu__probe_without_cpuid(void)
 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
 }
 
+static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
+
 static void __init fpu__init_system_early_generic(void)
 {
+	fpstate_reset(&x86_init_fpu);
+	current->thread.fpu = &x86_init_fpu;
+	set_thread_flag(TIF_NEED_FPU_LOAD);
+	x86_init_fpu.last_cpu = -1;
+
 	if (!boot_cpu_has(X86_FEATURE_CPUID) &&
 	    !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
 		if (fpu__probe_without_cpuid())
@@ -150,6 +157,8 @@ static void __init fpu__init_task_struct_size(void)
 {
 	int task_size = sizeof(struct task_struct);
 
+	task_size += sizeof(struct fpu);
+
 	/*
 	 * Subtract off the static size of the register state.
 	 * It potentially has a bunch of padding.
@@ -164,14 +173,9 @@ static void __init fpu__init_task_struct_size(void)
 
 	/*
 	 * We dynamically size 'struct fpu', so we require that
-	 * it be at the end of 'thread_struct' and that
-	 * 'thread_struct' be at the end of 'task_struct'.  If
-	 * you hit a compile error here, check the structure to
-	 * see if something got added to the end.
+	 * 'state' be at the end of 'it:
 	 */
 	CHECK_MEMBER_AT_END_OF(struct fpu, __fpstate);
-	CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
-	CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
 
 	arch_task_struct_size = task_size;
 }
@@ -213,7 +217,6 @@ static void __init fpu__init_system_xstate_size_legacy(void)
  */
 void __init fpu__init_system(void)
 {
-	fpstate_reset(x86_task_fpu(current));
 	fpu__init_system_early_generic();
 
 	/*
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 47694e391506..3ce4cce46f3f 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -103,7 +103,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 	dst->thread.vm86 = NULL;
 #endif
 	/* Drop the copied pointer to current's fpstate */
-	x86_task_fpu(dst)->fpstate = NULL;
+	dst->thread.fpu = NULL;
 
 	return 0;
 }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac1982893..4ecc0c6b1cb0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1646,22 +1646,15 @@ struct task_struct {
 	struct user_event_mm		*user_event_mm;
 #endif
 
-	/*
-	 * New fields for task_struct should be added above here, so that
-	 * they are included in the randomized portion of task_struct.
-	 */
-	randomized_struct_fields_end
-
 	/* CPU-specific state of this task: */
 	struct thread_struct		thread;
 
 	/*
-	 * WARNING: on x86, 'thread_struct' contains a variable-sized
-	 * structure.  It *MUST* be at the end of 'task_struct'.
-	 *
-	 * Do not put anything below here!
+	 * New fields for task_struct should be added above here, so that
+	 * they are included in the randomized portion of task_struct.
 	 */
-};
+	randomized_struct_fields_end
+} __attribute__ ((aligned (64)));
 
 #define TASK_REPORT_IDLE	(TASK_REPORT + 1)
 #define TASK_REPORT_MAX		(TASK_REPORT_IDLE << 1)
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (2 preceding siblings ...)
  2025-04-09 21:11 ` [PATCH 3/8] x86/fpu: Make task_struct::thread constant size Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-10  7:39   ` Peter Zijlstra
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-09 21:11 ` [PATCH 5/8] x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call Ingo Molnar
                   ` (11 subsequent siblings)
  15 siblings, 2 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar, Andy Lutomirski,
	Fenghua Yu, Dave Hansen, Uros Bizjak

As suggested by Oleg, remove the thread::fpu pointer, as we can
calculate it via x86_task_fpu() at compile-time.

This improves code generation a bit:

   kepler:~/tip> size vmlinux.before vmlinux.after
   text        data        bss        dec         hex        filename
   26475405    10435342    1740804    38651551    24dc69f    vmlinux.before
   26475339    10959630    1216516    38651485    24dc65d    vmlinux.after

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20240605083557.2051480-3-mingo@kernel.org
---
 arch/x86/include/asm/processor.h | 5 +----
 arch/x86/kernel/fpu/core.c       | 4 +---
 arch/x86/kernel/fpu/init.c       | 1 -
 arch/x86/kernel/process.c        | 2 --
 arch/x86/kernel/vmlinux.lds.S    | 4 ++++
 5 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 5ea7e5d2c4de..b7f7c9c83409 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -514,12 +514,9 @@ struct thread_struct {
 
 	struct thread_shstk	shstk;
 #endif
-
-	/* Floating point and extended processor state */
-	struct fpu		*fpu;
 };
 
-#define x86_task_fpu(task) ((task)->thread.fpu)
+#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
 
 /*
  * X86 doesn't need any embedded-FPU-struct quirks:
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 853a738fdf2d..974b276ff0da 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -600,13 +600,11 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	 * This is safe because task_struct size is a multiple of cacheline size.
 	 */
 	struct fpu *src_fpu = x86_task_fpu(current);
-	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
+	struct fpu *dst_fpu = x86_task_fpu(dst);
 
 	BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
 	BUG_ON(!src_fpu);
 
-	dst->thread.fpu = dst_fpu;
-
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
 
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 848ea79886ba..da41a1d2c40f 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -76,7 +76,6 @@ static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
 static void __init fpu__init_system_early_generic(void)
 {
 	fpstate_reset(&x86_init_fpu);
-	current->thread.fpu = &x86_init_fpu;
 	set_thread_flag(TIF_NEED_FPU_LOAD);
 	x86_init_fpu.last_cpu = -1;
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 3ce4cce46f3f..88868a90459e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -102,8 +102,6 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 #ifdef CONFIG_VM86
 	dst->thread.vm86 = NULL;
 #endif
-	/* Drop the copied pointer to current's fpstate */
-	dst->thread.fpu = NULL;
 
 	return 0;
 }
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ccdc45e5b759..d9ca2d1754da 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -181,6 +181,10 @@ SECTIONS
 		/* equivalent to task_pt_regs(&init_task) */
 		__top_init_kernel_stack = __end_init_stack - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE;
 
+		__x86_init_fpu_begin = .;
+		. = __x86_init_fpu_begin + 128*PAGE_SIZE;
+		__x86_init_fpu_end = .;
+
 #ifdef CONFIG_X86_32
 		/* 32 bit has nosave before _edata */
 		NOSAVE_DATA
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH 5/8] x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (3 preceding siblings ...)
  2025-04-09 21:11 ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-09 21:11 ` [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit Ingo Molnar
                   ` (10 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar

This encapsulates the fpu__drop() functionality better, and it
will also enable other changes that want to check a task for
PF_KTHREAD before calling x86_task_fpu().

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/fpu/sched.h | 2 +-
 arch/x86/kernel/fpu/core.c       | 4 +++-
 arch/x86/kernel/process.c        | 3 +--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index 1feaa68b7567..5fd12634bcc4 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -10,7 +10,7 @@
 #include <asm/trace/fpu.h>
 
 extern void save_fpregs_to_fpstate(struct fpu *fpu);
-extern void fpu__drop(struct fpu *fpu);
+extern void fpu__drop(struct task_struct *tsk);
 extern int  fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 		      unsigned long shstk_addr);
 extern void fpu_flush_thread(void);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 974b276ff0da..e4c20908ee49 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -681,8 +681,10 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
  * a state-restore is coming: either an explicit one,
  * or a reschedule.
  */
-void fpu__drop(struct fpu *fpu)
+void fpu__drop(struct task_struct *tsk)
 {
+	struct fpu *fpu = x86_task_fpu(tsk);
+
 	preempt_disable();
 
 	if (fpu == x86_task_fpu(current)) {
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 88868a90459e..5fb502c97b08 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -120,7 +120,6 @@ void arch_release_task_struct(struct task_struct *tsk)
 void exit_thread(struct task_struct *tsk)
 {
 	struct thread_struct *t = &tsk->thread;
-	struct fpu *fpu = x86_task_fpu(tsk);
 
 	if (test_thread_flag(TIF_IO_BITMAP))
 		io_bitmap_exit(tsk);
@@ -128,7 +127,7 @@ void exit_thread(struct task_struct *tsk)
 	free_vm86(t);
 
 	shstk_free(tsk);
-	fpu__drop(fpu);
+	fpu__drop(tsk);
 }
 
 static int set_new_tls(struct task_struct *p, unsigned long tls)
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (4 preceding siblings ...)
  2025-04-09 21:11 ` [PATCH 5/8] x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-11 15:22   ` Chang S. Bae
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-09 21:11 ` [PATCH 7/8] x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks Ingo Molnar
                   ` (9 subsequent siblings)
  15 siblings, 2 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar

fpu__drop() and arch_release_task_struct() calls x86_task_fpu()
unconditionally, while the FPU context area will not be present
if it's the init task, and should not be in use when it's some
other type of kthread.

Return early for PF_KTHREAD or PF_USER_WORKER tasks. The debug
warning in x86_task_fpu() will catch any kthreads attempting to
use the FPU save area.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/fpu/core.c | 8 +++++++-
 arch/x86/kernel/process.c  | 2 +-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index e4c20908ee49..4a2193892e5d 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -683,7 +683,13 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
  */
 void fpu__drop(struct task_struct *tsk)
 {
-	struct fpu *fpu = x86_task_fpu(tsk);
+	struct fpu *fpu;
+
+	/* PF_KTHREAD tasks do not use the FPU context area: */
+	if (tsk->flags & (PF_KTHREAD | PF_USER_WORKER))
+		return;
+
+	fpu = x86_task_fpu(tsk);
 
 	preempt_disable();
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 5fb502c97b08..de9df37c5d67 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -109,7 +109,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 #ifdef CONFIG_X86_64
 void arch_release_task_struct(struct task_struct *tsk)
 {
-	if (fpu_state_size_dynamic())
+	if (fpu_state_size_dynamic() && !(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
 		fpstate_free(x86_task_fpu(tsk));
 }
 #endif
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH 7/8] x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (5 preceding siblings ...)
  2025-04-09 21:11 ` [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-09 21:11 ` [PATCH 8/8] x86/fpu: Use 'fpstate' variable names consistently Ingo Molnar
                   ` (8 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar, Andy Lutomirski,
	Fenghua Yu, Dave Hansen, Uros Bizjak

init_task's FPU state initialization was a bit of a hack:

		__x86_init_fpu_begin = .;
		. = __x86_init_fpu_begin + 128*PAGE_SIZE;
		__x86_init_fpu_end = .;

But the init task isn't supposed to be using the FPU context
in any case, so remove the hack and add in some debug warnings.

As Linus noted in the discussion, the init task (and other
PF_KTHREAD tasks) *can* use the FPU via kernel_fpu_begin()/_end(),
but they don't need the context area because their FPU use is not
preemptible or reentrant, and they don't return to user-space.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20240605083557.2051480-4-mingo@kernel.org
---
 arch/x86/include/asm/processor.h |  6 +++++-
 arch/x86/kernel/fpu/core.c       | 15 +++++++++++----
 arch/x86/kernel/fpu/init.c       |  3 +--
 arch/x86/kernel/fpu/xstate.c     |  3 ---
 arch/x86/kernel/vmlinux.lds.S    |  4 ----
 5 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index b7f7c9c83409..eaa7214d6953 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -516,7 +516,11 @@ struct thread_struct {
 #endif
 };
 
-#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
+#ifdef CONFIG_X86_DEBUG_FPU
+extern struct fpu *x86_task_fpu(struct task_struct *task);
+#else
+# define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
+#endif
 
 /*
  * X86 doesn't need any embedded-FPU-struct quirks:
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4a2193892e5d..4d1a205b7ce2 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -51,6 +51,16 @@ static DEFINE_PER_CPU(bool, in_kernel_fpu);
  */
 DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
 
+#ifdef CONFIG_X86_DEBUG_FPU
+struct fpu *x86_task_fpu(struct task_struct *task)
+{
+	if (WARN_ON_ONCE(task->flags & PF_KTHREAD))
+		return NULL;
+
+	return (void *)task + sizeof(*task);
+}
+#endif
+
 /*
  * Can we use the FPU in kernel mode with the
  * whole "kernel_fpu_begin/end()" sequence?
@@ -599,11 +609,9 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	 *
 	 * This is safe because task_struct size is a multiple of cacheline size.
 	 */
-	struct fpu *src_fpu = x86_task_fpu(current);
-	struct fpu *dst_fpu = x86_task_fpu(dst);
+	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
 
 	BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
-	BUG_ON(!src_fpu);
 
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
@@ -666,7 +674,6 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	if (update_fpu_shstk(dst, ssp))
 		return 1;
 
-	trace_x86_fpu_copy_src(src_fpu);
 	trace_x86_fpu_copy_dst(dst_fpu);
 
 	return 0;
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index da41a1d2c40f..16b6611634c3 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -38,7 +38,7 @@ static void fpu__init_cpu_generic(void)
 	/* Flush out any pending x87 state: */
 #ifdef CONFIG_MATH_EMULATION
 	if (!boot_cpu_has(X86_FEATURE_FPU))
-		fpstate_init_soft(&x86_task_fpu(current)->fpstate->regs.soft);
+		;
 	else
 #endif
 		asm volatile ("fninit");
@@ -207,7 +207,6 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	fpu_kernel_cfg.default_size = size;
 	fpu_user_cfg.max_size = size;
 	fpu_user_cfg.default_size = size;
-	fpstate_reset(x86_task_fpu(current));
 }
 
 /*
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index ab2588b8f17f..00e87afa876d 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -834,9 +834,6 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
 	if (err)
 		goto out_disable;
 
-	/* Reset the state for the current task */
-	fpstate_reset(x86_task_fpu(current));
-
 	/*
 	 * Update info used for ptrace frames; use standard-format size and no
 	 * supervisor xstates:
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index d9ca2d1754da..ccdc45e5b759 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -181,10 +181,6 @@ SECTIONS
 		/* equivalent to task_pt_regs(&init_task) */
 		__top_init_kernel_stack = __end_init_stack - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE;
 
-		__x86_init_fpu_begin = .;
-		. = __x86_init_fpu_begin + 128*PAGE_SIZE;
-		__x86_init_fpu_end = .;
-
 #ifdef CONFIG_X86_32
 		/* 32 bit has nosave before _edata */
 		NOSAVE_DATA
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH 8/8] x86/fpu: Use 'fpstate' variable names consistently
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (6 preceding siblings ...)
  2025-04-09 21:11 ` [PATCH 7/8] x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks Ingo Molnar
@ 2025-04-09 21:11 ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  2025-04-22 16:11 ` [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Oleg Nesterov
                   ` (7 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Ingo Molnar @ 2025-04-09 21:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Ingo Molnar

A few uses of 'fps' snuck in, which is rather confusing
(to me) as it suggests frames-per-second. ;-)

Rename them to the canonical 'fpstate' name.

No change in functionality.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/fpu/api.h |  2 +-
 arch/x86/kernel/fpu/core.c     | 14 +++++++-------
 arch/x86/kernel/fpu/xstate.c   |  4 ++--
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index f42de5f05e7e..8e6848f55dcd 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -136,7 +136,7 @@ static inline void fpstate_free(struct fpu *fpu) { }
 #endif
 
 /* fpstate-related functions which are exported to KVM */
-extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature);
+extern void fpstate_clear_xstate_component(struct fpstate *fpstate, unsigned int xfeature);
 
 extern u64 xstate_get_guest_group_perm(void);
 
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4d1a205b7ce2..d0a45f6492cb 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -273,16 +273,16 @@ EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);
 
 void fpu_free_guest_fpstate(struct fpu_guest *gfpu)
 {
-	struct fpstate *fps = gfpu->fpstate;
+	struct fpstate *fpstate = gfpu->fpstate;
 
-	if (!fps)
+	if (!fpstate)
 		return;
 
-	if (WARN_ON_ONCE(!fps->is_valloc || !fps->is_guest || fps->in_use))
+	if (WARN_ON_ONCE(!fpstate->is_valloc || !fpstate->is_guest || fpstate->in_use))
 		return;
 
 	gfpu->fpstate = NULL;
-	vfree(fps);
+	vfree(fpstate);
 }
 EXPORT_SYMBOL_GPL(fpu_free_guest_fpstate);
 
@@ -333,12 +333,12 @@ EXPORT_SYMBOL_GPL(fpu_update_guest_xfd);
  */
 void fpu_sync_guest_vmexit_xfd_state(void)
 {
-	struct fpstate *fps = x86_task_fpu(current)->fpstate;
+	struct fpstate *fpstate = x86_task_fpu(current)->fpstate;
 
 	lockdep_assert_irqs_disabled();
 	if (fpu_state_size_dynamic()) {
-		rdmsrl(MSR_IA32_XFD, fps->xfd);
-		__this_cpu_write(xfd_state, fps->xfd);
+		rdmsrl(MSR_IA32_XFD, fpstate->xfd);
+		__this_cpu_write(xfd_state, fpstate->xfd);
 	}
 }
 EXPORT_SYMBOL_GPL(fpu_sync_guest_vmexit_xfd_state);
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 00e87afa876d..79ad768647f8 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1395,9 +1395,9 @@ void xrstors(struct xregs_state *xstate, u64 mask)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature)
+void fpstate_clear_xstate_component(struct fpstate *fpstate, unsigned int xfeature)
 {
-	void *addr = get_xsave_addr(&fps->regs.xsave, xfeature);
+	void *addr = get_xsave_addr(&fpstate->regs.xsave, xfeature);
 
 	if (addr)
 		memset(addr, 0, xstate_sizes[xfeature]);
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* Re: [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer
  2025-04-09 21:11 ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
@ 2025-04-10  7:39   ` Peter Zijlstra
  2025-04-10 10:10     ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  1 sibling, 1 reply; 43+ messages in thread
From: Peter Zijlstra @ 2025-04-10  7:39 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Andy Lutomirski, Fenghua Yu,
	Dave Hansen, Uros Bizjak

On Wed, Apr 09, 2025 at 11:11:23PM +0200, Ingo Molnar wrote:

> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 5ea7e5d2c4de..b7f7c9c83409 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -514,12 +514,9 @@ struct thread_struct {
>  
>  	struct thread_shstk	shstk;
>  #endif
> -
> -	/* Floating point and extended processor state */
> -	struct fpu		*fpu;
>  };
>  
> -#define x86_task_fpu(task) ((task)->thread.fpu)
> +#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))

Doesn't our FPU state need to be cacheline aligned? Looking at struct
fpu, it has a bunch of members that have __aligned__(64) on them, and as
such the whole of struct fpu will inherit this alignment requirement.

This means that both task and sizeof(*task) need to be cacheline aligned
for this to work.

Would it make sense to add something like:

static_assert(sizeof(struct task_struct) % 64 == 0);

And I didn't check, but isn't task a page pointer and as such always
page aligned?

^ permalink raw reply	[flat|nested] 43+ messages in thread
* Re: [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer
  2025-04-10  7:39   ` Peter Zijlstra
@ 2025-04-10 10:10     ` Ingo Molnar
  2025-04-10 10:30       ` Peter Zijlstra
                         ` (2 more replies)
  0 siblings, 3 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-10 10:10 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Andy Lutomirski, Fenghua Yu,
	Dave Hansen, Uros Bizjak


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, Apr 09, 2025 at 11:11:23PM +0200, Ingo Molnar wrote:
> 
> > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> > index 5ea7e5d2c4de..b7f7c9c83409 100644
> > --- a/arch/x86/include/asm/processor.h
> > +++ b/arch/x86/include/asm/processor.h
> > @@ -514,12 +514,9 @@ struct thread_struct {
> >  
> >  	struct thread_shstk	shstk;
> >  #endif
> > -
> > -	/* Floating point and extended processor state */
> > -	struct fpu		*fpu;
> >  };
> >  
> > -#define x86_task_fpu(task) ((task)->thread.fpu)
> > +#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
> 
> Doesn't our FPU state need to be cacheline aligned?

Yeah, and we do have a check for that:

+       BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);

And task_struct is allocated cache-aligned, which means when we do this 
in fpu_clone():

+       struct fpu *dst_fpu = (void *)dst + sizeof(*dst);

the FPU pointer is guaranteed to be cacheline aligned as well.

'dst' in that context is the new task_struct.

BTW., Oleg suggested in a previous discussion for us to replace the 
task->thread.fpu pointer with a build-time calculation - but I'm still 
not sure it's a good idea.

Thanks,

	Ingo

^ permalink raw reply	[flat|nested] 43+ messages in thread
* Re: [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer
  2025-04-10 10:10     ` Ingo Molnar
@ 2025-04-10 10:30       ` Peter Zijlstra
  2025-04-10 10:54         ` [PATCH] x86/fpu: Clarify FPU context cacheline alignment Ingo Molnar
  2025-04-10 10:51       ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
  2025-04-10 14:04       ` Oleg Nesterov
  2 siblings, 1 reply; 43+ messages in thread
From: Peter Zijlstra @ 2025-04-10 10:30 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Andy Lutomirski, Fenghua Yu,
	Dave Hansen, Uros Bizjak

On Thu, Apr 10, 2025 at 12:10:56PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Wed, Apr 09, 2025 at 11:11:23PM +0200, Ingo Molnar wrote:
> > 
> > > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> > > index 5ea7e5d2c4de..b7f7c9c83409 100644
> > > --- a/arch/x86/include/asm/processor.h
> > > +++ b/arch/x86/include/asm/processor.h
> > > @@ -514,12 +514,9 @@ struct thread_struct {
> > >  
> > >  	struct thread_shstk	shstk;
> > >  #endif
> > > -
> > > -	/* Floating point and extended processor state */
> > > -	struct fpu		*fpu;
> > >  };
> > >  
> > > -#define x86_task_fpu(task) ((task)->thread.fpu)
> > > +#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
> > 
> > Doesn't our FPU state need to be cacheline aligned?
> 
> Yeah, and we do have a check for that:
> 
> +       BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);

Ah, missed that. Clearly I need to improve my reading skillz :-)

^ permalink raw reply	[flat|nested] 43+ messages in thread
* Re: [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer
  2025-04-10 10:10     ` Ingo Molnar
  2025-04-10 10:30       ` Peter Zijlstra
@ 2025-04-10 10:51       ` Ingo Molnar
  2025-04-10 14:04       ` Oleg Nesterov
  2 siblings, 0 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-10 10:51 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Andy Lutomirski, Fenghua Yu,
	Dave Hansen, Uros Bizjak


* Ingo Molnar <mingo@kernel.org> wrote:

> BTW., Oleg suggested in a previous discussion for us to replace the 
> task->thread.fpu pointer with a build-time calculation - but I'm 
> still not sure it's a good idea.

Actually, I've implemented that already:

  arch/x86/include/asm/processor.h:# define x86_task_fpu(task)    ((struct fpu *)((void *)(task) + sizeof(*(task))))

... then promptly forgot about it. So never mind me. :-)

Thanks,

	Ingo

^ permalink raw reply	[flat|nested] 43+ messages in thread
* [PATCH] x86/fpu: Clarify FPU context cacheline alignment
  2025-04-10 10:30       ` Peter Zijlstra
@ 2025-04-10 10:54         ` Ingo Molnar
  2025-04-14  7:34           ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  0 siblings, 1 reply; 43+ messages in thread
From: Ingo Molnar @ 2025-04-10 10:54 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner, Chang S . Bae, Andy Lutomirski, Fenghua Yu,
	Dave Hansen, Uros Bizjak


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, Apr 10, 2025 at 12:10:56PM +0200, Ingo Molnar wrote:
> > 
> > * Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > > On Wed, Apr 09, 2025 at 11:11:23PM +0200, Ingo Molnar wrote:
> > > 
> > > > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> > > > index 5ea7e5d2c4de..b7f7c9c83409 100644
> > > > --- a/arch/x86/include/asm/processor.h
> > > > +++ b/arch/x86/include/asm/processor.h
> > > > @@ -514,12 +514,9 @@ struct thread_struct {
> > > >  
> > > >  	struct thread_shstk	shstk;
> > > >  #endif
> > > > -
> > > > -	/* Floating point and extended processor state */
> > > > -	struct fpu		*fpu;
> > > >  };
> > > >  
> > > > -#define x86_task_fpu(task) ((task)->thread.fpu)
> > > > +#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
> > > 
> > > Doesn't our FPU state need to be cacheline aligned?
> > 
> > Yeah, and we do have a check for that:
> > 
> > +       BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
> 
> Ah, missed that. Clearly I need to improve my reading skillz :-)

Admittedly it's written a bit obtusely - how about the patch below?

Thanks,

	Ingo

============================>
From: Ingo Molnar <mingo@kernel.org>
Date: Thu, 10 Apr 2025 12:52:16 +0200
Subject: [PATCH] x86/fpu: Clarify FPU context cacheline alignment

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Uros Bizjak <ubizjak@gmail.com>
---
 arch/x86/kernel/fpu/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index d0a45f6492cb..3a19877a314e 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -607,7 +607,8 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	 * We allocate the new FPU structure right after the end of the task struct.
 	 * task allocation size already took this into account.
 	 *
-	 * This is safe because task_struct size is a multiple of cacheline size.
+	 * This is safe because task_struct size is a multiple of cacheline size,
+	 * thus x86_task_fpu() will always be cacheline aligned as well.
 	 */
 	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
 

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* Re: [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer
  2025-04-10 10:10     ` Ingo Molnar
  2025-04-10 10:30       ` Peter Zijlstra
  2025-04-10 10:51       ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
@ 2025-04-10 14:04       ` Oleg Nesterov
  2 siblings, 0 replies; 43+ messages in thread
From: Oleg Nesterov @ 2025-04-10 14:04 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: Peter Zijlstra, linux-kernel, Andy Lutomirski, Dave Hansen,
	Brian Gerst, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae, Andy Lutomirski, Fenghua Yu,
	Dave Hansen, Uros Bizjak

On 04/10, Ingo Molnar wrote:
>
> * Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Wed, Apr 09, 2025 at 11:11:23PM +0200, Ingo Molnar wrote:
> >
> > > -#define x86_task_fpu(task) ((task)->thread.fpu)
> > > +#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
> >
> > Doesn't our FPU state need to be cacheline aligned?
>
> Yeah, and we do have a check for that:
>
> +       BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
>
> And task_struct is allocated cache-aligned, which means when we do this
> in fpu_clone():
>
> +       struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
>
> the FPU pointer is guaranteed to be cacheline aligned as well.
>
> 'dst' in that context is the new task_struct.
>
> BTW., Oleg suggested in a previous discussion for us to replace the
> task->thread.fpu pointer with a build-time calculation - but I'm still
> not sure it's a good idea.

To be honest, I forgot everything we discussed before ;)

But I have found this email,
https://lore.kernel.org/all/20240616105550.GA18292@redhat.com/
Perhaps

	#define X86_TASK_SIZE	\
		ALIGN(sizeof(struct task_struct), __alignof__(union fpregs_state))

and
	#define x86_task_fpu(task)	\
		((struct fpu *)((void *)(task) + X86_TASK_SIZE))

plus a bit more similar changes make more sense than
__attribute__ ((aligned (64))) for struct task_struct?

OK, even if yes, we can do this later on top of this series.

I'll try to read it tomorrow.

Oleg.


^ permalink raw reply	[flat|nested] 43+ messages in thread
* Re: [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit
  2025-04-09 21:11 ` [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit Ingo Molnar
@ 2025-04-11 15:22   ` Chang S. Bae
  2025-04-12  8:37     ` Ingo Molnar
  2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
  1 sibling, 1 reply; 43+ messages in thread
From: Chang S. Bae @ 2025-04-11 15:22 UTC (permalink / raw)
  To: Ingo Molnar, linux-kernel
  Cc: Andy Lutomirski, Dave Hansen, Brian Gerst, Peter Zijlstra,
	Borislav Petkov, H . Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Thomas Gleixner

On 4/9/2025 2:11 PM, Ingo Molnar wrote:
>   
>   void arch_release_task_struct(struct task_struct *tsk)
>   {
> -	if (fpu_state_size_dynamic())
> +	if (fpu_state_size_dynamic() && !(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
>   		fpstate_free(x86_task_fpu(tsk));
>   }

Looks like the AMX system couldn't boot properly, and I found that 
referencing tsk->flags here resolves the issue.

Thanks,
Chang

^ permalink raw reply	[flat|nested] 43+ messages in thread
* Re: [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit
  2025-04-11 15:22   ` Chang S. Bae
@ 2025-04-12  8:37     ` Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-12  8:37 UTC (permalink / raw)
  To: Chang S. Bae
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Oleg Nesterov, Thomas Gleixner


* Chang S. Bae <chang.seok.bae@intel.com> wrote:

> On 4/9/2025 2:11 PM, Ingo Molnar wrote:
> >   void arch_release_task_struct(struct task_struct *tsk)
> >   {
> > -	if (fpu_state_size_dynamic())
> > +	if (fpu_state_size_dynamic() && !(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
> >   		fpstate_free(x86_task_fpu(tsk));
> >   }
> 
> Looks like the AMX system couldn't boot properly, and I found that
> referencing tsk->flags here resolves the issue.

Indeed, fixed!

I've also added your Fixed-by tag to the patch:

  Fixed-by: Chang S. Bae <chang.seok.bae@intel.com>

Thanks,

	Ingo

==========>

 arch/x86/kernel/process.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index de9df37c5d67..7a1bfb61d86f 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -109,7 +109,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 #ifdef CONFIG_X86_64
 void arch_release_task_struct(struct task_struct *tsk)
 {
-	if (fpu_state_size_dynamic() && !(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
+	if (fpu_state_size_dynamic() && !(tsk->flags & (PF_KTHREAD | PF_USER_WORKER)))
 		fpstate_free(x86_task_fpu(tsk));
 }
 #endif

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Clarify FPU context cacheline alignment
  2025-04-10 10:54         ` [PATCH] x86/fpu: Clarify FPU context cacheline alignment Ingo Molnar
@ 2025-04-14  7:34           ` tip-bot2 for Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Peter Zijlstra, Ingo Molnar, Andy Lutomirski, Chang S. Bae,
	Fenghua Yu, H. Peter Anvin, Linus Torvalds, Oleg Nesterov, x86,
	linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     e3a52b67f54aa36ab21265eeea016460b5fe1c46
Gitweb:        https://git.kernel.org/tip/e3a52b67f54aa36ab21265eeea016460b5fe1c46
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Thu, 10 Apr 2025 12:52:16 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Clarify FPU context cacheline alignment

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/Z_ejggklB5-IWB5W@gmail.com
---
 arch/x86/kernel/fpu/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index d0a45f6..3a19877 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -607,7 +607,8 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	 * We allocate the new FPU structure right after the end of the task struct.
 	 * task allocation size already took this into account.
 	 *
-	 * This is safe because task_struct size is a multiple of cacheline size.
+	 * This is safe because task_struct size is a multiple of cacheline size,
+	 * thus x86_task_fpu() will always be cacheline aligned as well.
 	 */
 	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
 

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Use 'fpstate' variable names consistently
  2025-04-09 21:11 ` [PATCH 8/8] x86/fpu: Use 'fpstate' variable names consistently Ingo Molnar
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Ingo Molnar, Andy Lutomirski, Brian Gerst, Chang S. Bae,
	H. Peter Anvin, Linus Torvalds, Oleg Nesterov, Peter Zijlstra,
	x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     8b2a7a7294b34fa00adbecbd352ef19eb780261b
Gitweb:        https://git.kernel.org/tip/8b2a7a7294b34fa00adbecbd352ef19eb780261b
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:27 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Use 'fpstate' variable names consistently

A few uses of 'fps' snuck in, which is rather confusing
(to me) as it suggests frames-per-second. ;-)

Rename them to the canonical 'fpstate' name.

No change in functionality.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250409211127.3544993-9-mingo@kernel.org
---
 arch/x86/include/asm/fpu/api.h |  2 +-
 arch/x86/kernel/fpu/core.c     | 14 +++++++-------
 arch/x86/kernel/fpu/xstate.c   |  4 ++--
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index f42de5f..8e6848f 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -136,7 +136,7 @@ static inline void fpstate_free(struct fpu *fpu) { }
 #endif
 
 /* fpstate-related functions which are exported to KVM */
-extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature);
+extern void fpstate_clear_xstate_component(struct fpstate *fpstate, unsigned int xfeature);
 
 extern u64 xstate_get_guest_group_perm(void);
 
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4d1a205..d0a45f6 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -273,16 +273,16 @@ EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);
 
 void fpu_free_guest_fpstate(struct fpu_guest *gfpu)
 {
-	struct fpstate *fps = gfpu->fpstate;
+	struct fpstate *fpstate = gfpu->fpstate;
 
-	if (!fps)
+	if (!fpstate)
 		return;
 
-	if (WARN_ON_ONCE(!fps->is_valloc || !fps->is_guest || fps->in_use))
+	if (WARN_ON_ONCE(!fpstate->is_valloc || !fpstate->is_guest || fpstate->in_use))
 		return;
 
 	gfpu->fpstate = NULL;
-	vfree(fps);
+	vfree(fpstate);
 }
 EXPORT_SYMBOL_GPL(fpu_free_guest_fpstate);
 
@@ -333,12 +333,12 @@ EXPORT_SYMBOL_GPL(fpu_update_guest_xfd);
  */
 void fpu_sync_guest_vmexit_xfd_state(void)
 {
-	struct fpstate *fps = x86_task_fpu(current)->fpstate;
+	struct fpstate *fpstate = x86_task_fpu(current)->fpstate;
 
 	lockdep_assert_irqs_disabled();
 	if (fpu_state_size_dynamic()) {
-		rdmsrl(MSR_IA32_XFD, fps->xfd);
-		__this_cpu_write(xfd_state, fps->xfd);
+		rdmsrl(MSR_IA32_XFD, fpstate->xfd);
+		__this_cpu_write(xfd_state, fpstate->xfd);
 	}
 }
 EXPORT_SYMBOL_GPL(fpu_sync_guest_vmexit_xfd_state);
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 4c771b9..a288597 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1431,9 +1431,9 @@ void xrstors(struct xregs_state *xstate, u64 mask)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature)
+void fpstate_clear_xstate_component(struct fpstate *fpstate, unsigned int xfeature)
 {
-	void *addr = get_xsave_addr(&fps->regs.xsave, xfeature);
+	void *addr = get_xsave_addr(&fpstate->regs.xsave, xfeature);
 
 	if (addr)
 		memset(addr, 0, xstate_sizes[xfeature]);

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks
  2025-04-09 21:11 ` [PATCH 7/8] x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks Ingo Molnar
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Ingo Molnar, Andy Lutomirski, Brian Gerst, Chang S. Bae,
	Fenghua Yu, H. Peter Anvin, Linus Torvalds, Oleg Nesterov,
	Peter Zijlstra, Uros Bizjak, x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     22aafe3bcb67472effdea1ccf0df20280192bbaf
Gitweb:        https://git.kernel.org/tip/22aafe3bcb67472effdea1ccf0df20280192bbaf
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:26 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks

init_task's FPU state initialization was a bit of a hack:

		__x86_init_fpu_begin = .;
		. = __x86_init_fpu_begin + 128*PAGE_SIZE;
		__x86_init_fpu_end = .;

But the init task isn't supposed to be using the FPU context
in any case, so remove the hack and add in some debug warnings.

As Linus noted in the discussion, the init task (and other
PF_KTHREAD tasks) *can* use the FPU via kernel_fpu_begin()/_end(),
but they don't need the context area because their FPU use is not
preemptible or reentrant, and they don't return to user-space.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20250409211127.3544993-8-mingo@kernel.org
---
 arch/x86/include/asm/processor.h |  6 +++++-
 arch/x86/kernel/fpu/core.c       | 15 +++++++++++----
 arch/x86/kernel/fpu/init.c       |  3 +--
 arch/x86/kernel/fpu/xstate.c     |  3 ---
 arch/x86/kernel/vmlinux.lds.S    |  4 ----
 5 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index b7f7c9c..eaa7214 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -516,7 +516,11 @@ struct thread_struct {
 #endif
 };
 
-#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
+#ifdef CONFIG_X86_DEBUG_FPU
+extern struct fpu *x86_task_fpu(struct task_struct *task);
+#else
+# define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
+#endif
 
 /*
  * X86 doesn't need any embedded-FPU-struct quirks:
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 4a21938..4d1a205 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -51,6 +51,16 @@ static DEFINE_PER_CPU(bool, in_kernel_fpu);
  */
 DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
 
+#ifdef CONFIG_X86_DEBUG_FPU
+struct fpu *x86_task_fpu(struct task_struct *task)
+{
+	if (WARN_ON_ONCE(task->flags & PF_KTHREAD))
+		return NULL;
+
+	return (void *)task + sizeof(*task);
+}
+#endif
+
 /*
  * Can we use the FPU in kernel mode with the
  * whole "kernel_fpu_begin/end()" sequence?
@@ -599,11 +609,9 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	 *
 	 * This is safe because task_struct size is a multiple of cacheline size.
 	 */
-	struct fpu *src_fpu = x86_task_fpu(current);
-	struct fpu *dst_fpu = x86_task_fpu(dst);
+	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
 
 	BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
-	BUG_ON(!src_fpu);
 
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
@@ -666,7 +674,6 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	if (update_fpu_shstk(dst, ssp))
 		return 1;
 
-	trace_x86_fpu_copy_src(src_fpu);
 	trace_x86_fpu_copy_dst(dst_fpu);
 
 	return 0;
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index da41a1d..16b6611 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -38,7 +38,7 @@ static void fpu__init_cpu_generic(void)
 	/* Flush out any pending x87 state: */
 #ifdef CONFIG_MATH_EMULATION
 	if (!boot_cpu_has(X86_FEATURE_FPU))
-		fpstate_init_soft(&x86_task_fpu(current)->fpstate->regs.soft);
+		;
 	else
 #endif
 		asm volatile ("fninit");
@@ -207,7 +207,6 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	fpu_kernel_cfg.default_size = size;
 	fpu_user_cfg.max_size = size;
 	fpu_user_cfg.default_size = size;
-	fpstate_reset(x86_task_fpu(current));
 }
 
 /*
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 253da5a..4c771b9 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -870,9 +870,6 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
 	if (err)
 		goto out_disable;
 
-	/* Reset the state for the current task */
-	fpstate_reset(x86_task_fpu(current));
-
 	/*
 	 * Update info used for ptrace frames; use standard-format size and no
 	 * supervisor xstates:
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index d9ca2d1..ccdc45e 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -181,10 +181,6 @@ SECTIONS
 		/* equivalent to task_pt_regs(&init_task) */
 		__top_init_kernel_stack = __end_init_stack - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE;
 
-		__x86_init_fpu_begin = .;
-		. = __x86_init_fpu_begin + 128*PAGE_SIZE;
-		__x86_init_fpu_end = .;
-
 #ifdef CONFIG_X86_32
 		/* 32 bit has nosave before _edata */
 		NOSAVE_DATA

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit
  2025-04-09 21:11 ` [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit Ingo Molnar
  2025-04-11 15:22   ` Chang S. Bae
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  1 sibling, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Ingo Molnar, Andy Lutomirski, Brian Gerst, H. Peter Anvin,
	Linus Torvalds, Oleg Nesterov, Peter Zijlstra, x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     c360bdc593b8a8b6e94166026728764085919cff
Gitweb:        https://git.kernel.org/tip/c360bdc593b8a8b6e94166026728764085919cff
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:25 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit

fpu__drop() and arch_release_task_struct() calls x86_task_fpu()
unconditionally, while the FPU context area will not be present
if it's the init task, and should not be in use when it's some
other type of kthread.

Return early for PF_KTHREAD or PF_USER_WORKER tasks. The debug
warning in x86_task_fpu() will catch any kthreads attempting to
use the FPU save area.

Fixed-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250409211127.3544993-7-mingo@kernel.org
---
 arch/x86/kernel/fpu/core.c | 8 +++++++-
 arch/x86/kernel/process.c  | 2 +-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index e4c2090..4a21938 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -683,7 +683,13 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
  */
 void fpu__drop(struct task_struct *tsk)
 {
-	struct fpu *fpu = x86_task_fpu(tsk);
+	struct fpu *fpu;
+
+	/* PF_KTHREAD tasks do not use the FPU context area: */
+	if (tsk->flags & (PF_KTHREAD | PF_USER_WORKER))
+		return;
+
+	fpu = x86_task_fpu(tsk);
 
 	preempt_disable();
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 5fb502c..7a1bfb6 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -109,7 +109,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 #ifdef CONFIG_X86_64
 void arch_release_task_struct(struct task_struct *tsk)
 {
-	if (fpu_state_size_dynamic())
+	if (fpu_state_size_dynamic() && !(tsk->flags & (PF_KTHREAD | PF_USER_WORKER)))
 		fpstate_free(x86_task_fpu(tsk));
 }
 #endif

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call
  2025-04-09 21:11 ` [PATCH 5/8] x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call Ingo Molnar
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Ingo Molnar, Andy Lutomirski, Brian Gerst, Chang S. Bae,
	H. Peter Anvin, Linus Torvalds, Oleg Nesterov, Peter Zijlstra,
	x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     ec2227e03a46a162f2721917262adc553b212e2d
Gitweb:        https://git.kernel.org/tip/ec2227e03a46a162f2721917262adc553b212e2d
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:24 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call

This encapsulates the fpu__drop() functionality better, and it
will also enable other changes that want to check a task for
PF_KTHREAD before calling x86_task_fpu().

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250409211127.3544993-6-mingo@kernel.org
---
 arch/x86/include/asm/fpu/sched.h | 2 +-
 arch/x86/kernel/fpu/core.c       | 4 +++-
 arch/x86/kernel/process.c        | 3 +--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index 1feaa68..5fd1263 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -10,7 +10,7 @@
 #include <asm/trace/fpu.h>
 
 extern void save_fpregs_to_fpstate(struct fpu *fpu);
-extern void fpu__drop(struct fpu *fpu);
+extern void fpu__drop(struct task_struct *tsk);
 extern int  fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 		      unsigned long shstk_addr);
 extern void fpu_flush_thread(void);
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 974b276..e4c2090 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -681,8 +681,10 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
  * a state-restore is coming: either an explicit one,
  * or a reschedule.
  */
-void fpu__drop(struct fpu *fpu)
+void fpu__drop(struct task_struct *tsk)
 {
+	struct fpu *fpu = x86_task_fpu(tsk);
+
 	preempt_disable();
 
 	if (fpu == x86_task_fpu(current)) {
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 88868a9..5fb502c 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -120,7 +120,6 @@ void arch_release_task_struct(struct task_struct *tsk)
 void exit_thread(struct task_struct *tsk)
 {
 	struct thread_struct *t = &tsk->thread;
-	struct fpu *fpu = x86_task_fpu(tsk);
 
 	if (test_thread_flag(TIF_IO_BITMAP))
 		io_bitmap_exit(tsk);
@@ -128,7 +127,7 @@ void exit_thread(struct task_struct *tsk)
 	free_vm86(t);
 
 	shstk_free(tsk);
-	fpu__drop(fpu);
+	fpu__drop(tsk);
 }
 
 static int set_new_tls(struct task_struct *p, unsigned long tls)

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Remove the thread::fpu pointer
  2025-04-09 21:11 ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
  2025-04-10  7:39   ` Peter Zijlstra
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  1 sibling, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Oleg Nesterov, Ingo Molnar, Andy Lutomirski, Brian Gerst,
	Chang S. Bae, H. Peter Anvin, Linus Torvalds, Peter Zijlstra,
	Uros Bizjak, x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     55bc30f2e34dcc17a370d1f6c1c992be107c4502
Gitweb:        https://git.kernel.org/tip/55bc30f2e34dcc17a370d1f6c1c992be107c4502
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:23 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Remove the thread::fpu pointer

As suggested by Oleg, remove the thread::fpu pointer, as we can
calculate it via x86_task_fpu() at compile-time.

This improves code generation a bit:

   kepler:~/tip> size vmlinux.before vmlinux.after
   text        data        bss        dec         hex        filename
   26475405    10435342    1740804    38651551    24dc69f    vmlinux.before
   26475339    10959630    1216516    38651485    24dc65d    vmlinux.after

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20250409211127.3544993-5-mingo@kernel.org
---
 arch/x86/include/asm/processor.h | 5 +----
 arch/x86/kernel/fpu/core.c       | 4 +---
 arch/x86/kernel/fpu/init.c       | 1 -
 arch/x86/kernel/process.c        | 2 --
 arch/x86/kernel/vmlinux.lds.S    | 4 ++++
 5 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 5ea7e5d..b7f7c9c 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -514,12 +514,9 @@ struct thread_struct {
 
 	struct thread_shstk	shstk;
 #endif
-
-	/* Floating point and extended processor state */
-	struct fpu		*fpu;
 };
 
-#define x86_task_fpu(task) ((task)->thread.fpu)
+#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
 
 /*
  * X86 doesn't need any embedded-FPU-struct quirks:
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 853a738..974b276 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -600,13 +600,11 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	 * This is safe because task_struct size is a multiple of cacheline size.
 	 */
 	struct fpu *src_fpu = x86_task_fpu(current);
-	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
+	struct fpu *dst_fpu = x86_task_fpu(dst);
 
 	BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
 	BUG_ON(!src_fpu);
 
-	dst->thread.fpu = dst_fpu;
-
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
 
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 848ea79..da41a1d 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -76,7 +76,6 @@ static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
 static void __init fpu__init_system_early_generic(void)
 {
 	fpstate_reset(&x86_init_fpu);
-	current->thread.fpu = &x86_init_fpu;
 	set_thread_flag(TIF_NEED_FPU_LOAD);
 	x86_init_fpu.last_cpu = -1;
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 3ce4cce..88868a9 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -102,8 +102,6 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 #ifdef CONFIG_VM86
 	dst->thread.vm86 = NULL;
 #endif
-	/* Drop the copied pointer to current's fpstate */
-	dst->thread.fpu = NULL;
 
 	return 0;
 }
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ccdc45e..d9ca2d1 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -181,6 +181,10 @@ SECTIONS
 		/* equivalent to task_pt_regs(&init_task) */
 		__top_init_kernel_stack = __end_init_stack - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE;
 
+		__x86_init_fpu_begin = .;
+		. = __x86_init_fpu_begin + 128*PAGE_SIZE;
+		__x86_init_fpu_end = .;
+
 #ifdef CONFIG_X86_32
 		/* 32 bit has nosave before _edata */
 		NOSAVE_DATA

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Make task_struct::thread constant size
  2025-04-09 21:11 ` [PATCH 3/8] x86/fpu: Make task_struct::thread constant size Ingo Molnar
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Ingo Molnar, Andy Lutomirski, Brian Gerst, Chang S. Bae,
	H. Peter Anvin, Linus Torvalds, x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     cb7ca40a3882360ce87191793449d48df0b29184
Gitweb:        https://git.kernel.org/tip/cb7ca40a3882360ce87191793449d48df0b29184
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:22 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Make task_struct::thread constant size

Turn thread.fpu into a pointer. Since most FPU code internals work by passing
around the FPU pointer already, the code generation impact is small.

This allows us to remove the old kludge of task_struct being variable size:

  struct task_struct {

       ...
       /*
        * New fields for task_struct should be added above here, so that
        * they are included in the randomized portion of task_struct.
        */
       randomized_struct_fields_end

       /* CPU-specific state of this task: */
       struct thread_struct            thread;

       /*
        * WARNING: on x86, 'thread_struct' contains a variable-sized
        * structure.  It *MUST* be at the end of 'task_struct'.
        *
        * Do not put anything below here!
        */
  };

... which creates a number of problems, such as requiring thread_struct to be
the last member of the struct - not allowing it to be struct-randomized, etc.

But the primary motivation is to allow the decoupling of task_struct from
hardware details (<asm/processor.h> in particular), and to eventually allow
the per-task infrastructure:

   DECLARE_PER_TASK(type, name);
   ...
   per_task(current, name) = val;

... which requires task_struct to be a constant size struct.

The fpu_thread_struct_whitelist() quirk to hardened usercopy can be removed,
now that the FPU structure is not embedded in the task struct anymore, which
reduces text footprint a bit.

Fixed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250409211127.3544993-4-mingo@kernel.org
---
 arch/x86/include/asm/processor.h | 20 +++++++++-----------
 arch/x86/kernel/fpu/core.c       | 23 ++++++++++++-----------
 arch/x86/kernel/fpu/init.c       | 17 ++++++++++-------
 arch/x86/kernel/process.c        |  2 +-
 include/linux/sched.h            | 15 ++++-----------
 5 files changed, 36 insertions(+), 41 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 2f631e0..5ea7e5d 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -516,21 +516,19 @@ struct thread_struct {
 #endif
 
 	/* Floating point and extended processor state */
-	struct fpu		fpu;
-	/*
-	 * WARNING: 'fpu' is dynamically-sized.  It *MUST* be at
-	 * the end.
-	 */
+	struct fpu		*fpu;
 };
 
-#define x86_task_fpu(task) (&(task)->thread.fpu)
-
-extern void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size);
+#define x86_task_fpu(task) ((task)->thread.fpu)
 
-static inline void arch_thread_struct_whitelist(unsigned long *offset,
-						unsigned long *size)
+/*
+ * X86 doesn't need any embedded-FPU-struct quirks:
+ */
+static inline void
+arch_thread_struct_whitelist(unsigned long *offset, unsigned long *size)
 {
-	fpu_thread_struct_whitelist(offset, size);
+	*offset = 0;
+	*size = 0;
 }
 
 static inline void
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index dc6d7f9..853a738 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -593,8 +593,19 @@ static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp)
 int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	      unsigned long ssp)
 {
+	/*
+	 * We allocate the new FPU structure right after the end of the task struct.
+	 * task allocation size already took this into account.
+	 *
+	 * This is safe because task_struct size is a multiple of cacheline size.
+	 */
 	struct fpu *src_fpu = x86_task_fpu(current);
-	struct fpu *dst_fpu = x86_task_fpu(dst);
+	struct fpu *dst_fpu = (void *)dst + sizeof(*dst);
+
+	BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);
+	BUG_ON(!src_fpu);
+
+	dst->thread.fpu = dst_fpu;
 
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
@@ -664,16 +675,6 @@ int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 }
 
 /*
- * Whitelist the FPU register state embedded into task_struct for hardened
- * usercopy.
- */
-void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size)
-{
-	*offset = offsetof(struct thread_struct, fpu.__fpstate.regs);
-	*size = fpu_kernel_cfg.default_size;
-}
-
-/*
  * Drops current FPU state: deactivates the fpregs and
  * the fpstate. NOTE: it still leaves previous contents
  * in the fpregs in the eager-FPU case.
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index ad5cb29..848ea79 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -71,8 +71,15 @@ static bool __init fpu__probe_without_cpuid(void)
 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
 }
 
+static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
+
 static void __init fpu__init_system_early_generic(void)
 {
+	fpstate_reset(&x86_init_fpu);
+	current->thread.fpu = &x86_init_fpu;
+	set_thread_flag(TIF_NEED_FPU_LOAD);
+	x86_init_fpu.last_cpu = -1;
+
 	if (!boot_cpu_has(X86_FEATURE_CPUID) &&
 	    !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
 		if (fpu__probe_without_cpuid())
@@ -150,6 +157,8 @@ static void __init fpu__init_task_struct_size(void)
 {
 	int task_size = sizeof(struct task_struct);
 
+	task_size += sizeof(struct fpu);
+
 	/*
 	 * Subtract off the static size of the register state.
 	 * It potentially has a bunch of padding.
@@ -164,14 +173,9 @@ static void __init fpu__init_task_struct_size(void)
 
 	/*
 	 * We dynamically size 'struct fpu', so we require that
-	 * it be at the end of 'thread_struct' and that
-	 * 'thread_struct' be at the end of 'task_struct'.  If
-	 * you hit a compile error here, check the structure to
-	 * see if something got added to the end.
+	 * 'state' be at the end of 'it:
 	 */
 	CHECK_MEMBER_AT_END_OF(struct fpu, __fpstate);
-	CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu);
-	CHECK_MEMBER_AT_END_OF(struct task_struct, thread);
 
 	arch_task_struct_size = task_size;
 }
@@ -213,7 +217,6 @@ static void __init fpu__init_system_xstate_size_legacy(void)
  */
 void __init fpu__init_system(void)
 {
-	fpstate_reset(x86_task_fpu(current));
 	fpu__init_system_early_generic();
 
 	/*
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 47694e3..3ce4cce 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -103,7 +103,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 	dst->thread.vm86 = NULL;
 #endif
 	/* Drop the copied pointer to current's fpstate */
-	x86_task_fpu(dst)->fpstate = NULL;
+	dst->thread.fpu = NULL;
 
 	return 0;
 }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac19..4ecc0c6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1646,22 +1646,15 @@ struct task_struct {
 	struct user_event_mm		*user_event_mm;
 #endif
 
-	/*
-	 * New fields for task_struct should be added above here, so that
-	 * they are included in the randomized portion of task_struct.
-	 */
-	randomized_struct_fields_end
-
 	/* CPU-specific state of this task: */
 	struct thread_struct		thread;
 
 	/*
-	 * WARNING: on x86, 'thread_struct' contains a variable-sized
-	 * structure.  It *MUST* be at the end of 'task_struct'.
-	 *
-	 * Do not put anything below here!
+	 * New fields for task_struct should be added above here, so that
+	 * they are included in the randomized portion of task_struct.
 	 */
-};
+	randomized_struct_fields_end
+} __attribute__ ((aligned (64)));
 
 #define TASK_REPORT_IDLE	(TASK_REPORT + 1)
 #define TASK_REPORT_MAX		(TASK_REPORT_IDLE << 1)

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu()
  2025-04-09 21:11 ` [PATCH 2/8] x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu() Ingo Molnar
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Ingo Molnar, Andy Lutomirski, Brian Gerst, Chang S. Bae,
	H. Peter Anvin, Linus Torvalds, Oleg Nesterov, x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     e3bfa3859936da3edd1e16d0b74fdaaa19bb5087
Gitweb:        https://git.kernel.org/tip/e3bfa3859936da3edd1e16d0b74fdaaa19bb5087
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:21 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu()

This will make the removal of the task_struct::thread.fpu array
easier.

No change in functionality - code generated before and after this
commit is identical on x86-defconfig:

  kepler:~/tip> diff -up vmlinux.before.asm vmlinux.after.asm
  kepler:~/tip>

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250409211127.3544993-3-mingo@kernel.org
---
 arch/x86/include/asm/fpu/sched.h |  2 +-
 arch/x86/kernel/fpu/context.h    |  4 ++--
 arch/x86/kernel/fpu/core.c       | 30 +++++++++++++++---------------
 arch/x86/kernel/fpu/init.c       |  8 ++++----
 arch/x86/kernel/fpu/regset.c     | 22 +++++++++++-----------
 arch/x86/kernel/fpu/signal.c     | 18 +++++++++---------
 arch/x86/kernel/fpu/xstate.c     | 22 +++++++++++-----------
 arch/x86/kernel/fpu/xstate.h     |  6 +++---
 arch/x86/kernel/process.c        |  6 +++---
 arch/x86/kernel/signal.c         |  6 +++---
 arch/x86/kernel/traps.c          |  2 +-
 arch/x86/math-emu/fpu_aux.c      |  2 +-
 arch/x86/math-emu/fpu_entry.c    |  4 ++--
 arch/x86/math-emu/fpu_system.h   |  2 +-
 arch/x86/mm/extable.c            |  2 +-
 15 files changed, 68 insertions(+), 68 deletions(-)

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index c485f19..1feaa68 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -41,7 +41,7 @@ static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
 {
 	if (cpu_feature_enabled(X86_FEATURE_FPU) &&
 	    !(old->flags & (PF_KTHREAD | PF_USER_WORKER))) {
-		struct fpu *old_fpu = &old->thread.fpu;
+		struct fpu *old_fpu = x86_task_fpu(old);
 
 		save_fpregs_to_fpstate(old_fpu);
 		/*
diff --git a/arch/x86/kernel/fpu/context.h b/arch/x86/kernel/fpu/context.h
index f6d856b..10d0a72 100644
--- a/arch/x86/kernel/fpu/context.h
+++ b/arch/x86/kernel/fpu/context.h
@@ -53,7 +53,7 @@ static inline void fpregs_activate(struct fpu *fpu)
 /* Internal helper for switch_fpu_return() and signal frame setup */
 static inline void fpregs_restore_userregs(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	int cpu = smp_processor_id();
 
 	if (WARN_ON_ONCE(current->flags & (PF_KTHREAD | PF_USER_WORKER)))
@@ -67,7 +67,7 @@ static inline void fpregs_restore_userregs(void)
 		 * If PKRU is enabled, then the PKRU value is already
 		 * correct because it was either set in switch_to() or in
 		 * flush_thread(). So it is excluded because it might be
-		 * not up to date in current->thread.fpu.xsave state.
+		 * not up to date in current->thread.fpu->xsave state.
 		 *
 		 * XFD state is handled in restore_fpregs_from_fpstate().
 		 */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 91d6341..dc6d7f9 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -211,7 +211,7 @@ static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 		return;
 
 	spin_lock_irq(&current->sighand->siglock);
-	fpuperm = &current->group_leader->thread.fpu.guest_perm;
+	fpuperm = &x86_task_fpu(current->group_leader)->guest_perm;
 	perm = fpuperm->__state_perm;
 
 	/* First fpstate allocation locks down permissions. */
@@ -323,7 +323,7 @@ EXPORT_SYMBOL_GPL(fpu_update_guest_xfd);
  */
 void fpu_sync_guest_vmexit_xfd_state(void)
 {
-	struct fpstate *fps = current->thread.fpu.fpstate;
+	struct fpstate *fps = x86_task_fpu(current)->fpstate;
 
 	lockdep_assert_irqs_disabled();
 	if (fpu_state_size_dynamic()) {
@@ -337,7 +337,7 @@ EXPORT_SYMBOL_GPL(fpu_sync_guest_vmexit_xfd_state);
 int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
 {
 	struct fpstate *guest_fps = guest_fpu->fpstate;
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	struct fpstate *cur_fps = fpu->fpstate;
 
 	fpregs_lock();
@@ -438,7 +438,7 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 	if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER)) &&
 	    !test_thread_flag(TIF_NEED_FPU_LOAD)) {
 		set_thread_flag(TIF_NEED_FPU_LOAD);
-		save_fpregs_to_fpstate(&current->thread.fpu);
+		save_fpregs_to_fpstate(x86_task_fpu(current));
 	}
 	__cpu_invalidate_fpregs_state();
 
@@ -467,7 +467,7 @@ EXPORT_SYMBOL_GPL(kernel_fpu_end);
  */
 void fpu_sync_fpstate(struct fpu *fpu)
 {
-	WARN_ON_FPU(fpu != &current->thread.fpu);
+	WARN_ON_FPU(fpu != x86_task_fpu(current));
 
 	fpregs_lock();
 	trace_x86_fpu_before_save(fpu);
@@ -552,7 +552,7 @@ void fpstate_reset(struct fpu *fpu)
 static inline void fpu_inherit_perms(struct fpu *dst_fpu)
 {
 	if (fpu_state_size_dynamic()) {
-		struct fpu *src_fpu = &current->group_leader->thread.fpu;
+		struct fpu *src_fpu = x86_task_fpu(current->group_leader);
 
 		spin_lock_irq(&current->sighand->siglock);
 		/* Fork also inherits the permissions of the parent */
@@ -572,7 +572,7 @@ static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp)
 	if (!ssp)
 		return 0;
 
-	xstate = get_xsave_addr(&dst->thread.fpu.fpstate->regs.xsave,
+	xstate = get_xsave_addr(&x86_task_fpu(dst)->fpstate->regs.xsave,
 				XFEATURE_CET_USER);
 
 	/*
@@ -593,8 +593,8 @@ static int update_fpu_shstk(struct task_struct *dst, unsigned long ssp)
 int fpu_clone(struct task_struct *dst, unsigned long clone_flags, bool minimal,
 	      unsigned long ssp)
 {
-	struct fpu *src_fpu = &current->thread.fpu;
-	struct fpu *dst_fpu = &dst->thread.fpu;
+	struct fpu *src_fpu = x86_task_fpu(current);
+	struct fpu *dst_fpu = x86_task_fpu(dst);
 
 	/* The new task's FPU state cannot be valid in the hardware. */
 	dst_fpu->last_cpu = -1;
@@ -686,7 +686,7 @@ void fpu__drop(struct fpu *fpu)
 {
 	preempt_disable();
 
-	if (fpu == &current->thread.fpu) {
+	if (fpu == x86_task_fpu(current)) {
 		/* Ignore delayed exceptions from user space */
 		asm volatile("1: fwait\n"
 			     "2:\n"
@@ -720,7 +720,7 @@ static inline void restore_fpregs_from_init_fpstate(u64 features_mask)
  */
 static void fpu_reset_fpregs(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	fpregs_lock();
 	__fpu_invalidate_fpregs_state(fpu);
@@ -749,7 +749,7 @@ static void fpu_reset_fpregs(void)
  */
 void fpu__clear_user_states(struct fpu *fpu)
 {
-	WARN_ON_FPU(fpu != &current->thread.fpu);
+	WARN_ON_FPU(fpu != x86_task_fpu(current));
 
 	fpregs_lock();
 	if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
@@ -782,7 +782,7 @@ void fpu__clear_user_states(struct fpu *fpu)
 
 void fpu_flush_thread(void)
 {
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 	fpu_reset_fpregs();
 }
 /*
@@ -823,7 +823,7 @@ void fpregs_lock_and_load(void)
  */
 void fpregs_assert_state_consistent(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		return;
@@ -835,7 +835,7 @@ EXPORT_SYMBOL_GPL(fpregs_assert_state_consistent);
 
 void fpregs_mark_activate(void)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	fpregs_activate(fpu);
 	fpu->last_cpu = smp_processor_id();
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 998a08f..ad5cb29 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -38,7 +38,7 @@ static void fpu__init_cpu_generic(void)
 	/* Flush out any pending x87 state: */
 #ifdef CONFIG_MATH_EMULATION
 	if (!boot_cpu_has(X86_FEATURE_FPU))
-		fpstate_init_soft(&current->thread.fpu.fpstate->regs.soft);
+		fpstate_init_soft(&x86_task_fpu(current)->fpstate->regs.soft);
 	else
 #endif
 		asm volatile ("fninit");
@@ -154,7 +154,7 @@ static void __init fpu__init_task_struct_size(void)
 	 * Subtract off the static size of the register state.
 	 * It potentially has a bunch of padding.
 	 */
-	task_size -= sizeof(current->thread.fpu.__fpstate.regs);
+	task_size -= sizeof(union fpregs_state);
 
 	/*
 	 * Add back the dynamically-calculated register state
@@ -204,7 +204,7 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	fpu_kernel_cfg.default_size = size;
 	fpu_user_cfg.max_size = size;
 	fpu_user_cfg.default_size = size;
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 }
 
 /*
@@ -213,7 +213,7 @@ static void __init fpu__init_system_xstate_size_legacy(void)
  */
 void __init fpu__init_system(void)
 {
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 	fpu__init_system_early_generic();
 
 	/*
diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 887b0b8..0986c22 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -45,7 +45,7 @@ int regset_xregset_fpregs_active(struct task_struct *target, const struct user_r
  */
 static void sync_fpstate(struct fpu *fpu)
 {
-	if (fpu == &current->thread.fpu)
+	if (fpu == x86_task_fpu(current))
 		fpu_sync_fpstate(fpu);
 }
 
@@ -63,7 +63,7 @@ static void fpu_force_restore(struct fpu *fpu)
 	 * Only stopped child tasks can be used to modify the FPU
 	 * state in the fpstate buffer:
 	 */
-	WARN_ON_FPU(fpu == &current->thread.fpu);
+	WARN_ON_FPU(fpu == x86_task_fpu(current));
 
 	__fpu_invalidate_fpregs_state(fpu);
 }
@@ -71,7 +71,7 @@ static void fpu_force_restore(struct fpu *fpu)
 int xfpregs_get(struct task_struct *target, const struct user_regset *regset,
 		struct membuf to)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 
 	if (!cpu_feature_enabled(X86_FEATURE_FXSR))
 		return -ENODEV;
@@ -91,7 +91,7 @@ int xfpregs_set(struct task_struct *target, const struct user_regset *regset,
 		unsigned int pos, unsigned int count,
 		const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct fxregs_state newstate;
 	int ret;
 
@@ -133,7 +133,7 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
 	if (!cpu_feature_enabled(X86_FEATURE_XSAVE))
 		return -ENODEV;
 
-	sync_fpstate(&target->thread.fpu);
+	sync_fpstate(x86_task_fpu(target));
 
 	copy_xstate_to_uabi_buf(to, target, XSTATE_COPY_XSAVE);
 	return 0;
@@ -143,7 +143,7 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
 		  unsigned int pos, unsigned int count,
 		  const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct xregs_state *tmpbuf = NULL;
 	int ret;
 
@@ -187,7 +187,7 @@ int ssp_active(struct task_struct *target, const struct user_regset *regset)
 int ssp_get(struct task_struct *target, const struct user_regset *regset,
 	    struct membuf to)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct cet_user_state *cetregs;
 
 	if (!cpu_feature_enabled(X86_FEATURE_USER_SHSTK) ||
@@ -214,7 +214,7 @@ int ssp_set(struct task_struct *target, const struct user_regset *regset,
 	    unsigned int pos, unsigned int count,
 	    const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct xregs_state *xsave = &fpu->fpstate->regs.xsave;
 	struct cet_user_state *cetregs;
 	unsigned long user_ssp;
@@ -368,7 +368,7 @@ static void __convert_from_fxsr(struct user_i387_ia32_struct *env,
 void
 convert_from_fxsr(struct user_i387_ia32_struct *env, struct task_struct *tsk)
 {
-	__convert_from_fxsr(env, tsk, &tsk->thread.fpu.fpstate->regs.fxsave);
+	__convert_from_fxsr(env, tsk, &x86_task_fpu(tsk)->fpstate->regs.fxsave);
 }
 
 void convert_to_fxsr(struct fxregs_state *fxsave,
@@ -401,7 +401,7 @@ void convert_to_fxsr(struct fxregs_state *fxsave,
 int fpregs_get(struct task_struct *target, const struct user_regset *regset,
 	       struct membuf to)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct user_i387_ia32_struct env;
 	struct fxregs_state fxsave, *fx;
 
@@ -433,7 +433,7 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset,
 	       unsigned int pos, unsigned int count,
 	       const void *kbuf, const void __user *ubuf)
 {
-	struct fpu *fpu = &target->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(target);
 	struct user_i387_ia32_struct env;
 	int ret;
 
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 6c69cb2..b8b4fa9 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -43,13 +43,13 @@ static inline bool check_xstate_in_sigframe(struct fxregs_state __user *fxbuf,
 	 * fpstate layout with out copying the extended state information
 	 * in the memory layout.
 	 */
-	if (__get_user(magic2, (__u32 __user *)(fpstate + current->thread.fpu.fpstate->user_size)))
+	if (__get_user(magic2, (__u32 __user *)(fpstate + x86_task_fpu(current)->fpstate->user_size)))
 		return false;
 
 	if (likely(magic2 == FP_XSTATE_MAGIC2))
 		return true;
 setfx:
-	trace_x86_fpu_xstate_check_failed(&current->thread.fpu);
+	trace_x86_fpu_xstate_check_failed(x86_task_fpu(current));
 
 	/* Set the parameters for fx only state */
 	fx_sw->magic1 = 0;
@@ -64,13 +64,13 @@ setfx:
 static inline bool save_fsave_header(struct task_struct *tsk, void __user *buf)
 {
 	if (use_fxsr()) {
-		struct xregs_state *xsave = &tsk->thread.fpu.fpstate->regs.xsave;
+		struct xregs_state *xsave = &x86_task_fpu(tsk)->fpstate->regs.xsave;
 		struct user_i387_ia32_struct env;
 		struct _fpstate_32 __user *fp = buf;
 
 		fpregs_lock();
 		if (!test_thread_flag(TIF_NEED_FPU_LOAD))
-			fxsave(&tsk->thread.fpu.fpstate->regs.fxsave);
+			fxsave(&x86_task_fpu(tsk)->fpstate->regs.fxsave);
 		fpregs_unlock();
 
 		convert_from_fxsr(&env, tsk);
@@ -184,7 +184,7 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf, u32 pk
 bool copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size, u32 pkru)
 {
 	struct task_struct *tsk = current;
-	struct fpstate *fpstate = tsk->thread.fpu.fpstate;
+	struct fpstate *fpstate = x86_task_fpu(tsk)->fpstate;
 	bool ia32_fxstate = (buf != buf_fx);
 	int ret;
 
@@ -272,7 +272,7 @@ static int __restore_fpregs_from_user(void __user *buf, u64 ufeatures,
  */
 static bool restore_fpregs_from_user(void __user *buf, u64 xrestore, bool fx_only)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	int ret;
 
 	/* Restore enabled features only. */
@@ -332,7 +332,7 @@ static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
 			      bool ia32_fxstate)
 {
 	struct task_struct *tsk = current;
-	struct fpu *fpu = &tsk->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(tsk);
 	struct user_i387_ia32_struct env;
 	bool success, fx_only = false;
 	union fpregs_state *fpregs;
@@ -452,7 +452,7 @@ static inline unsigned int xstate_sigframe_size(struct fpstate *fpstate)
  */
 bool fpu__restore_sig(void __user *buf, int ia32_frame)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	void __user *buf_fx = buf;
 	bool ia32_fxstate = false;
 	bool success = false;
@@ -499,7 +499,7 @@ unsigned long
 fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
 		     unsigned long *buf_fx, unsigned long *size)
 {
-	unsigned long frame_size = xstate_sigframe_size(current->thread.fpu.fpstate);
+	unsigned long frame_size = xstate_sigframe_size(x86_task_fpu(current)->fpstate);
 
 	*buf_fx = sp = round_down(sp - frame_size, 64);
 	if (ia32_frame && use_fxsr()) {
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 46c45e2..253da5a 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -763,7 +763,7 @@ static void __init fpu__init_disable_system_xstate(unsigned int legacy_size)
 	 */
 	init_fpstate.xfd = 0;
 
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 }
 
 /*
@@ -871,7 +871,7 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
 		goto out_disable;
 
 	/* Reset the state for the current task */
-	fpstate_reset(&current->thread.fpu);
+	fpstate_reset(x86_task_fpu(current));
 
 	/*
 	 * Update info used for ptrace frames; use standard-format size and no
@@ -945,7 +945,7 @@ void fpu__resume_cpu(void)
 	}
 
 	if (fpu_state_size_dynamic())
-		wrmsrl(MSR_IA32_XFD, current->thread.fpu.fpstate->xfd);
+		wrmsrl(MSR_IA32_XFD, x86_task_fpu(current)->fpstate->xfd);
 }
 
 /*
@@ -1227,8 +1227,8 @@ out:
 void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk,
 			     enum xstate_copy_mode copy_mode)
 {
-	__copy_xstate_to_uabi_buf(to, tsk->thread.fpu.fpstate,
-				  tsk->thread.fpu.fpstate->user_xfeatures,
+	__copy_xstate_to_uabi_buf(to, x86_task_fpu(tsk)->fpstate,
+				  x86_task_fpu(tsk)->fpstate->user_xfeatures,
 				  tsk->thread.pkru, copy_mode);
 }
 
@@ -1368,7 +1368,7 @@ int copy_uabi_from_kernel_to_xstate(struct fpstate *fpstate, const void *kbuf, u
 int copy_sigframe_from_user_to_xstate(struct task_struct *tsk,
 				      const void __user *ubuf)
 {
-	return copy_uabi_to_xstate(tsk->thread.fpu.fpstate, NULL, ubuf, &tsk->thread.pkru);
+	return copy_uabi_to_xstate(x86_task_fpu(tsk)->fpstate, NULL, ubuf, &tsk->thread.pkru);
 }
 
 static bool validate_independent_components(u64 mask)
@@ -1462,7 +1462,7 @@ static bool xstate_op_valid(struct fpstate *fpstate, u64 mask, bool rstor)
 	  * The XFD MSR does not match fpstate->xfd. That's invalid when
 	  * the passed in fpstate is current's fpstate.
 	  */
-	if (fpstate->xfd == current->thread.fpu.fpstate->xfd)
+	if (fpstate->xfd == x86_task_fpu(current)->fpstate->xfd)
 		return false;
 
 	/*
@@ -1539,7 +1539,7 @@ void fpstate_free(struct fpu *fpu)
 static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
 			   unsigned int usize, struct fpu_guest *guest_fpu)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 	struct fpstate *curfps, *newfps = NULL;
 	unsigned int fpsize;
 	bool in_use;
@@ -1632,7 +1632,7 @@ static int __xstate_request_perm(u64 permitted, u64 requested, bool guest)
 	 * AVX512.
 	 */
 	bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
-	struct fpu *fpu = &current->group_leader->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current->group_leader);
 	struct fpu_state_perm *perm;
 	unsigned int ksize, usize;
 	u64 mask;
@@ -1735,7 +1735,7 @@ int __xfd_enable_feature(u64 xfd_err, struct fpu_guest *guest_fpu)
 		return -EPERM;
 	}
 
-	fpu = &current->group_leader->thread.fpu;
+	fpu = x86_task_fpu(current->group_leader);
 	perm = guest_fpu ? &fpu->guest_perm : &fpu->perm;
 	ksize = perm->__state_size;
 	usize = perm->__user_state_size;
@@ -1840,7 +1840,7 @@ long fpu_xstate_prctl(int option, unsigned long arg2)
  */
 static void avx512_status(struct seq_file *m, struct task_struct *task)
 {
-	unsigned long timestamp = READ_ONCE(task->thread.fpu.avx512_timestamp);
+	unsigned long timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp);
 	long delta;
 
 	if (!timestamp) {
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 0fd34f5..9a3a8cc 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -22,7 +22,7 @@ static inline void xstate_init_xcomp_bv(struct xregs_state *xsave, u64 mask)
 
 static inline u64 xstate_get_group_perm(bool guest)
 {
-	struct fpu *fpu = &current->group_leader->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current->group_leader);
 	struct fpu_state_perm *perm;
 
 	/* Pairs with WRITE_ONCE() in xstate_request_perm() */
@@ -288,7 +288,7 @@ static inline int xsave_to_user_sigframe(struct xregs_state __user *buf, u32 pkr
 	 * internally, e.g. PKRU. That's user space ABI and also required
 	 * to allow the signal handler to modify PKRU.
 	 */
-	struct fpstate *fpstate = current->thread.fpu.fpstate;
+	struct fpstate *fpstate = x86_task_fpu(current)->fpstate;
 	u64 mask = fpstate->user_xfeatures;
 	u32 lmask;
 	u32 hmask;
@@ -322,7 +322,7 @@ static inline int xrstor_from_user_sigframe(struct xregs_state __user *buf, u64 
 	u32 hmask = mask >> 32;
 	int err;
 
-	xfd_validate_state(current->thread.fpu.fpstate, mask, true);
+	xfd_validate_state(x86_task_fpu(current)->fpstate, mask, true);
 
 	stac();
 	XSTATE_OP(XRSTOR, xstate, lmask, hmask, err);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 962c3ce..47694e3 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -103,7 +103,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 	dst->thread.vm86 = NULL;
 #endif
 	/* Drop the copied pointer to current's fpstate */
-	dst->thread.fpu.fpstate = NULL;
+	x86_task_fpu(dst)->fpstate = NULL;
 
 	return 0;
 }
@@ -112,7 +112,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 void arch_release_task_struct(struct task_struct *tsk)
 {
 	if (fpu_state_size_dynamic())
-		fpstate_free(&tsk->thread.fpu);
+		fpstate_free(x86_task_fpu(tsk));
 }
 #endif
 
@@ -122,7 +122,7 @@ void arch_release_task_struct(struct task_struct *tsk)
 void exit_thread(struct task_struct *tsk)
 {
 	struct thread_struct *t = &tsk->thread;
-	struct fpu *fpu = &t->fpu;
+	struct fpu *fpu = x86_task_fpu(tsk);
 
 	if (test_thread_flag(TIF_IO_BITMAP))
 		io_bitmap_exit(tsk);
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 5f44103..2404233 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -255,7 +255,7 @@ static void
 handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 {
 	bool stepping, failed;
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(current);
 
 	if (v8086_mode(regs))
 		save_v86_state((struct kernel_vm86_regs *) regs, VM86_SIGNAL);
@@ -423,14 +423,14 @@ bool sigaltstack_size_valid(size_t ss_size)
 	if (!fpu_state_size_dynamic() && !strict_sigaltstack_size)
 		return true;
 
-	fsize += current->group_leader->thread.fpu.perm.__user_state_size;
+	fsize += x86_task_fpu(current->group_leader)->perm.__user_state_size;
 	if (likely(ss_size > fsize))
 		return true;
 
 	if (strict_sigaltstack_size)
 		return ss_size > fsize;
 
-	mask = current->group_leader->thread.fpu.perm.__state_perm;
+	mask = x86_task_fpu(current->group_leader)->perm.__state_perm;
 	if (mask & XFEATURE_MASK_USER_DYNAMIC)
 		return ss_size > fsize;
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 9f88b8a..f48325d 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1295,7 +1295,7 @@ DEFINE_IDTENTRY_RAW(exc_debug)
 static void math_error(struct pt_regs *regs, int trapnr)
 {
 	struct task_struct *task = current;
-	struct fpu *fpu = &task->thread.fpu;
+	struct fpu *fpu = x86_task_fpu(task);
 	int si_code;
 	char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
 						"simd exception";
diff --git a/arch/x86/math-emu/fpu_aux.c b/arch/x86/math-emu/fpu_aux.c
index d62662b..5f253ae 100644
--- a/arch/x86/math-emu/fpu_aux.c
+++ b/arch/x86/math-emu/fpu_aux.c
@@ -53,7 +53,7 @@ void fpstate_init_soft(struct swregs_state *soft)
 
 void finit(void)
 {
-	fpstate_init_soft(&current->thread.fpu.fpstate->regs.soft);
+	fpstate_init_soft(&x86_task_fpu(current)->fpstate->regs.soft);
 }
 
 /*
diff --git a/arch/x86/math-emu/fpu_entry.c b/arch/x86/math-emu/fpu_entry.c
index 91c52ea..5034df6 100644
--- a/arch/x86/math-emu/fpu_entry.c
+++ b/arch/x86/math-emu/fpu_entry.c
@@ -641,7 +641,7 @@ int fpregs_soft_set(struct task_struct *target,
 		    unsigned int pos, unsigned int count,
 		    const void *kbuf, const void __user *ubuf)
 {
-	struct swregs_state *s387 = &target->thread.fpu.fpstate->regs.soft;
+	struct swregs_state *s387 = &x86_task_fpu(target)->fpstate->regs.soft;
 	void *space = s387->st_space;
 	int ret;
 	int offset, other, i, tags, regnr, tag, newtop;
@@ -692,7 +692,7 @@ int fpregs_soft_get(struct task_struct *target,
 		    const struct user_regset *regset,
 		    struct membuf to)
 {
-	struct swregs_state *s387 = &target->thread.fpu.fpstate->regs.soft;
+	struct swregs_state *s387 = &x86_task_fpu(target)->fpstate->regs.soft;
 	const void *space = s387->st_space;
 	int offset = (S387->ftop & 7) * 10, other = 80 - offset;
 
diff --git a/arch/x86/math-emu/fpu_system.h b/arch/x86/math-emu/fpu_system.h
index eec3e48..5e238e9 100644
--- a/arch/x86/math-emu/fpu_system.h
+++ b/arch/x86/math-emu/fpu_system.h
@@ -73,7 +73,7 @@ static inline bool seg_writable(struct desc_struct *d)
 	return (d->type & SEG_TYPE_EXECUTE_MASK) == SEG_TYPE_WRITABLE;
 }
 
-#define I387			(&current->thread.fpu.fpstate->regs)
+#define I387			(&x86_task_fpu(current)->fpstate->regs)
 #define FPU_info		(I387->soft.info)
 
 #define FPU_CS			(*(unsigned short *) &(FPU_info->regs->cs))
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 51986e8..bf8dab1 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -111,7 +111,7 @@ static bool ex_handler_sgx(const struct exception_table_entry *fixup,
 
 /*
  * Handler for when we fail to restore a task's FPU state.  We should never get
- * here because the FPU state of a task using the FPU (task->thread.fpu.state)
+ * here because the FPU state of a task using the FPU (struct fpu::fpstate)
  * should always be valid.  However, past bugs have allowed userspace to set
  * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn().
  * These caused XRSTOR to fail when switching to the task, leaking the FPU

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/merge] x86/fpu: Introduce the x86_task_fpu() helper method
  2025-04-09 21:11 ` [PATCH 1/8] x86/fpu: Introduce the x86_task_fpu() helper method Ingo Molnar
@ 2025-04-14  7:34   ` tip-bot2 for Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Ingo Molnar @ 2025-04-14  7:34 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Ingo Molnar, Andy Lutomirski, Brian Gerst, Chang S. Bae,
	H. Peter Anvin, Linus Torvalds, Oleg Nesterov, Peter Zijlstra,
	x86, linux-kernel

The following commit has been merged into the x86/merge branch of tip:

Commit-ID:     77fbccede633a5565cae084348b5459f6849086d
Gitweb:        https://git.kernel.org/tip/77fbccede633a5565cae084348b5459f6849086d
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Wed, 09 Apr 2025 23:11:20 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 14 Apr 2025 08:18:29 +02:00

x86/fpu: Introduce the x86_task_fpu() helper method

The per-task FPU context/save area is allocated right
next to task_struct, currently in a variable-size
array via task_struct::thread.fpu[], but we plan to
fully hide it from the C type scope.

Introduce the x86_task_fpu() accessor that gets to the
FPU context pointer explicitly from the task pointer.

Right now this is a simple (task)->thread.fpu wrapper.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250409211127.3544993-2-mingo@kernel.org
---
 arch/x86/include/asm/processor.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 5d2f7e5..2f631e0 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -523,6 +523,8 @@ struct thread_struct {
 	 */
 };
 
+#define x86_task_fpu(task) (&(task)->thread.fpu)
+
 extern void fpu_thread_struct_whitelist(unsigned long *offset, unsigned long *size);
 
 static inline void arch_thread_struct_whitelist(unsigned long *offset,

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* Re: [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (7 preceding siblings ...)
  2025-04-09 21:11 ` [PATCH 8/8] x86/fpu: Use 'fpstate' variable names consistently Ingo Molnar
@ 2025-04-22 16:11 ` Oleg Nesterov
  2025-04-22 20:09   ` Ingo Molnar
  2025-04-22 17:01 ` question about switch_fpu_prepare/switch_fpu_finish Oleg Nesterov
                   ` (6 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Oleg Nesterov @ 2025-04-22 16:11 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae

Ingo, sorry for delay.

So just in case, the whole series looks good to me. I am going to send a
couple of minor cleanups on top of it, but let me ask first if I missed
something or not.

- x86_init_fpu is not really used after 4/8, it can be killed

- DEFINE_EVENT(x86_fpu, x86_fpu_copy_src) can be killed after 7/8

- arch_dup_task_struct() still does

	/* init_task is not dynamically sized (incomplete FPU state) */
	if (unlikely(src == &init_task))
		memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(init_task), 0);
	else
		memcpy(dst, src, arch_task_struct_size);

  and I don't understand why do we need to check src == &init_task. It seems
  that we can always do

	memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(struct task_struct), 0);

  or even just

	memcpy(dst, src, sizeof(struct task_struct));

  fpu_clone() will initialize the "dst_fpu" memory correctly.

- fpu__drop() does

	/* PF_KTHREAD tasks do not use the FPU context area: */
	if (tsk->flags & (PF_KTHREAD | PF_USER_WORKER))
		return;

  and this is correct. But perhaps

	if (test_tsk_thread_flag(tsk, TIF_NEED_FPU_LOAD))
		return;

  makes more sense? PF_KTHREAD's should never clear TIF_NEED_FPU_LOAD,
  and this way we can avoid the unnecessary "fwait" if, say, the exiting
  task does context_switch() at least once on its way to exit_thread().

- Finally, with or without these changes, it seems that the
  switch_fpu_prepare() + switch_fpu_finish() logic can be simplified,
  I'll write another email.


^ permalink raw reply	[flat|nested] 43+ messages in thread
* question about switch_fpu_prepare/switch_fpu_finish
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (8 preceding siblings ...)
  2025-04-22 16:11 ` [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Oleg Nesterov
@ 2025-04-22 17:01 ` Oleg Nesterov
  2025-04-22 20:11   ` Ingo Molnar
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 1/6] x86/fpu: simplify the switch_fpu_prepare() + switch_fpu_finish() logic Oleg Nesterov
                   ` (5 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Oleg Nesterov @ 2025-04-22 17:01 UTC (permalink / raw)
  To: Ingo Molnar, Linus Torvalds
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Thomas Gleixner,
	Chang S . Bae

I must have missed something, but I can't understand this logic, it
seems unnecessarily complicated today.

1. Now that switch_fpu_finish() doesn't load the FPU state, I think it
   can be folded into switch_fpu_prepare().

2. But the main question is that I fail to understand why
   __switch_to() -> switch_fpu_finish() uses the "next" task to set
   TIF_NEED_FPU_LOAD.

   I think that set_tsk_thread_flag(prev_p, TIF_NEED_FPU_LOAD) makes
   more sense.

   Just in case, note that fpu_clone() sets TIF_NEED_FPU_LOAD, so
   we should not worry about the 1st __switch_to(next_p).

IOW, can you explain why the (untested) patch below could be wrong?

We can even remove the PF_KTHREAD check in switch_fpu_prepare(), kthreads
should never clear TIF_NEED_FPU_LOAD...

Oleg.
---

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index 5fd12634bcc4..cdd60f434289 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -54,18 +54,10 @@ static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
 		 */
 		old_fpu->last_cpu = cpu;
 
+		set_tsk_thread_flag(old, TIF_NEED_FPU_LOAD);
+
 		trace_x86_fpu_regs_deactivated(old_fpu);
 	}
 }
 
-/*
- * Delay loading of the complete FPU state until the return to userland.
- * PKRU is handled separately.
- */
-static inline void switch_fpu_finish(struct task_struct *new)
-{
-	if (cpu_feature_enabled(X86_FEATURE_FPU))
-		set_tsk_thread_flag(new, TIF_NEED_FPU_LOAD);
-}
-
 #endif /* _ASM_X86_FPU_SCHED_H */
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 4636ef359973..b398a6ef2923 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -208,8 +208,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 
 	raw_cpu_write(current_task, next_p);
 
-	switch_fpu_finish(next_p);
-
 	/* Load the Intel cache allocation PQR MSR. */
 	resctrl_sched_in(next_p);
 
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 7196ca7048be..e8262e637ea4 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -671,8 +671,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	raw_cpu_write(current_task, next_p);
 	raw_cpu_write(cpu_current_top_of_stack, task_top_of_stack(next_p));
 
-	switch_fpu_finish(next_p);
-
 	/* Reload sp0. */
 	update_task_stack(next_p);
 


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* Re: [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu
  2025-04-22 16:11 ` [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Oleg Nesterov
@ 2025-04-22 20:09   ` Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-22 20:09 UTC (permalink / raw)
  To: Oleg Nesterov
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae


* Oleg Nesterov <oleg@redhat.com> wrote:

> Ingo, sorry for delay.
> 
> So just in case, the whole series looks good to me. I am going to send a
> couple of minor cleanups on top of it,

Great, please do!

> [...] but let me ask first if I missed something or not.

You probably didn't. :-)

> - x86_init_fpu is not really used after 4/8, it can be killed

Indeed!

> 
> - DEFINE_EVENT(x86_fpu, x86_fpu_copy_src) can be killed after 7/8

Agreed.

> - arch_dup_task_struct() still does
> 
> 	/* init_task is not dynamically sized (incomplete FPU state) */
> 	if (unlikely(src == &init_task))
> 		memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(init_task), 0);
> 	else
> 		memcpy(dst, src, arch_task_struct_size);
> 
>   and I don't understand why do we need to check src == &init_task. It seems
>   that we can always do
> 
> 	memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(struct task_struct), 0);
> 
>   or even just
> 
> 	memcpy(dst, src, sizeof(struct task_struct));
>
>   fpu_clone() will initialize the "dst_fpu" memory correctly.

Unecessary paranoia on my part, please send a patch to simplify this.

> - fpu__drop() does
> 
> 	/* PF_KTHREAD tasks do not use the FPU context area: */
> 	if (tsk->flags & (PF_KTHREAD | PF_USER_WORKER))
> 		return;
> 
>   and this is correct. But perhaps
> 
> 	if (test_tsk_thread_flag(tsk, TIF_NEED_FPU_LOAD))
> 		return;
> 
>   makes more sense? PF_KTHREAD's should never clear TIF_NEED_FPU_LOAD,
>   and this way we can avoid the unnecessary "fwait" if, say, the exiting
>   task does context_switch() at least once on its way to exit_thread().

I think you are right here as well.

> - Finally, with or without these changes, it seems that the
>   switch_fpu_prepare() + switch_fpu_finish() logic can be simplified,
>   I'll write another email.

Thank you!

	Ingo

^ permalink raw reply	[flat|nested] 43+ messages in thread
* Re: question about switch_fpu_prepare/switch_fpu_finish
  2025-04-22 17:01 ` question about switch_fpu_prepare/switch_fpu_finish Oleg Nesterov
@ 2025-04-22 20:11   ` Ingo Molnar
  0 siblings, 0 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-04-22 20:11 UTC (permalink / raw)
  To: Oleg Nesterov
  Cc: Linus Torvalds, linux-kernel, Andy Lutomirski, Dave Hansen,
	Brian Gerst, Peter Zijlstra, Borislav Petkov, H . Peter Anvin,
	Thomas Gleixner, Chang S . Bae


* Oleg Nesterov <oleg@redhat.com> wrote:

> I must have missed something, but I can't understand this logic, it
> seems unnecessarily complicated today.
> 
> 1. Now that switch_fpu_finish() doesn't load the FPU state, I think it
>    can be folded into switch_fpu_prepare().

Agreed.

> 2. But the main question is that I fail to understand why
>    __switch_to() -> switch_fpu_finish() uses the "next" task to set
>    TIF_NEED_FPU_LOAD.
> 
>    I think that set_tsk_thread_flag(prev_p, TIF_NEED_FPU_LOAD) makes
>    more sense.
> 
>    Just in case, note that fpu_clone() sets TIF_NEED_FPU_LOAD, so
>    we should not worry about the 1st __switch_to(next_p).
> 
> IOW, can you explain why the (untested) patch below could be wrong?

I think your patch should work.

> We can even remove the PF_KTHREAD check in switch_fpu_prepare(), kthreads
> should never clear TIF_NEED_FPU_LOAD...

Agreed.

Thanks,

	Ingo

^ permalink raw reply	[flat|nested] 43+ messages in thread
* [PATCH tip/x86/fpu 1/6] x86/fpu: simplify the switch_fpu_prepare() + switch_fpu_finish() logic
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (9 preceding siblings ...)
  2025-04-22 17:01 ` question about switch_fpu_prepare/switch_fpu_finish Oleg Nesterov
@ 2025-05-03 14:38 ` Oleg Nesterov
  2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Simplify " tip-bot2 for Oleg Nesterov
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 2/6] x86/fpu: kill x86_init_fpu Oleg Nesterov
                   ` (4 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Oleg Nesterov @ 2025-05-03 14:38 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae

Now that switch_fpu_finish() doesn't load the FPU state, it makes more
sense to fold it into switch_fpu_prepare() renamed to switch_fpu(), and
more importantly, use the "prev_p" task as a target for TIF_NEED_FPU_LOAD.
It doesn't make any sense to delay set_tsk_thread_flag(TIF_NEED_FPU_LOAD)
until "prev_p" is scheduled again.

There is no worry about the very first context switch, fpu_clone() must
always set TIF_NEED_FPU_LOAD.

Also, shift the test_tsk_thread_flag(TIF_NEED_FPU_LOAD) from the callers
to switch_fpu().

Note that the "PF_KTHREAD | PF_USER_WORKER" check can be removed but
this deserves a separate patch which can change more functions, say,
kernel_fpu_begin_mask().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/include/asm/fpu/sched.h | 34 +++++++++-----------------------
 arch/x86/kernel/process_32.c     |  5 +----
 arch/x86/kernel/process_64.c     |  5 +----
 3 files changed, 11 insertions(+), 33 deletions(-)

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index 5fd12634bcc4..c060549c6c94 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -18,31 +18,25 @@ extern void fpu_flush_thread(void);
 /*
  * FPU state switching for scheduling.
  *
- * This is a two-stage process:
+ * switch_fpu() saves the old state and sets TIF_NEED_FPU_LOAD if
+ * TIF_NEED_FPU_LOAD is not set.  This is done within the context
+ * of the old process.
  *
- *  - switch_fpu_prepare() saves the old state.
- *    This is done within the context of the old process.
- *
- *  - switch_fpu_finish() sets TIF_NEED_FPU_LOAD; the floating point state
- *    will get loaded on return to userspace, or when the kernel needs it.
- *
- * If TIF_NEED_FPU_LOAD is cleared then the CPU's FPU registers
- * are saved in the current thread's FPU register state.
- *
- * If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not
- * hold current()'s FPU registers. It is required to load the
+ * Once TIF_NEED_FPU_LOAD is set, it is required to load the
  * registers before returning to userland or using the content
  * otherwise.
  *
  * The FPU context is only stored/restored for a user task and
  * PF_KTHREAD is used to distinguish between kernel and user threads.
  */
-static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
+static inline void switch_fpu(struct task_struct *old, int cpu)
 {
-	if (cpu_feature_enabled(X86_FEATURE_FPU) &&
+	if (!test_tsk_thread_flag(old, TIF_NEED_FPU_LOAD) &&
+	    cpu_feature_enabled(X86_FEATURE_FPU) &&
 	    !(old->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		struct fpu *old_fpu = x86_task_fpu(old);
 
+		set_tsk_thread_flag(old, TIF_NEED_FPU_LOAD);
 		save_fpregs_to_fpstate(old_fpu);
 		/*
 		 * The save operation preserved register state, so the
@@ -50,7 +44,7 @@ static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
 		 * current CPU number in @old_fpu, so the next return
 		 * to user space can avoid the FPU register restore
 		 * when is returns on the same CPU and still owns the
-		 * context.
+		 * context. See fpregs_restore_userregs().
 		 */
 		old_fpu->last_cpu = cpu;
 
@@ -58,14 +52,4 @@ static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
 	}
 }
 
-/*
- * Delay loading of the complete FPU state until the return to userland.
- * PKRU is handled separately.
- */
-static inline void switch_fpu_finish(struct task_struct *new)
-{
-	if (cpu_feature_enabled(X86_FEATURE_FPU))
-		set_tsk_thread_flag(new, TIF_NEED_FPU_LOAD);
-}
-
 #endif /* _ASM_X86_FPU_SCHED_H */
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 4636ef359973..9bd4fa694da5 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -160,8 +160,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 
 	/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
 
-	if (!test_tsk_thread_flag(prev_p, TIF_NEED_FPU_LOAD))
-		switch_fpu_prepare(prev_p, cpu);
+	switch_fpu(prev_p, cpu);
 
 	/*
 	 * Save away %gs. No need to save %fs, as it was saved on the
@@ -208,8 +207,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 
 	raw_cpu_write(current_task, next_p);
 
-	switch_fpu_finish(next_p);
-
 	/* Load the Intel cache allocation PQR MSR. */
 	resctrl_sched_in(next_p);
 
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 7196ca7048be..d55310d3133c 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -616,8 +616,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ENTRY) &&
 		     this_cpu_read(hardirq_stack_inuse));
 
-	if (!test_tsk_thread_flag(prev_p, TIF_NEED_FPU_LOAD))
-		switch_fpu_prepare(prev_p, cpu);
+	switch_fpu(prev_p, cpu);
 
 	/* We must save %fs and %gs before load_TLS() because
 	 * %fs and %gs may be cleared by load_TLS().
@@ -671,8 +670,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	raw_cpu_write(current_task, next_p);
 	raw_cpu_write(cpu_current_top_of_stack, task_top_of_stack(next_p));
 
-	switch_fpu_finish(next_p);
-
 	/* Reload sp0. */
 	update_task_stack(next_p);
 
-- 
2.25.1.362.g51ebf55


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH tip/x86/fpu 2/6] x86/fpu: kill x86_init_fpu
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (10 preceding siblings ...)
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 1/6] x86/fpu: simplify the switch_fpu_prepare() + switch_fpu_finish() logic Oleg Nesterov
@ 2025-05-03 14:38 ` Oleg Nesterov
  2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Remove x86_init_fpu tip-bot2 for Oleg Nesterov
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 3/6] x86/fpu: kill DEFINE_EVENT(x86_fpu, x86_fpu_copy_src) Oleg Nesterov
                   ` (3 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Oleg Nesterov @ 2025-05-03 14:38 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae

It is not actually used after the commit 55bc30f2e34d ("x86/fpu: Remove
the thread::fpu pointer").

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/kernel/fpu/init.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 2d9b5e677559..6bb3e35c40e2 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -71,13 +71,9 @@ static bool __init fpu__probe_without_cpuid(void)
 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
 }
 
-static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
-
 static void __init fpu__init_system_early_generic(void)
 {
-	fpstate_reset(&x86_init_fpu);
 	set_thread_flag(TIF_NEED_FPU_LOAD);
-	x86_init_fpu.last_cpu = -1;
 
 	if (!boot_cpu_has(X86_FEATURE_CPUID) &&
 	    !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {
-- 
2.25.1.362.g51ebf55


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH tip/x86/fpu 3/6] x86/fpu: kill DEFINE_EVENT(x86_fpu, x86_fpu_copy_src)
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (11 preceding siblings ...)
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 2/6] x86/fpu: kill x86_init_fpu Oleg Nesterov
@ 2025-05-03 14:38 ` Oleg Nesterov
  2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Remove " tip-bot2 for Oleg Nesterov
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 4/6] x86/fpu: arch_dup_task_struct: always use memcpy_and_pad() Oleg Nesterov
                   ` (2 subsequent siblings)
  15 siblings, 1 reply; 43+ messages in thread
From: Oleg Nesterov @ 2025-05-03 14:38 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae

trace_x86_fpu_copy_src() has no users after the commit 22aafe3bcb67
("x86/fpu: Remove init_task FPU state dependencies, add debugging
 warning for PF_KTHREAD tasks").

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/include/asm/trace/fpu.h | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/x86/include/asm/trace/fpu.h b/arch/x86/include/asm/trace/fpu.h
index 4645a6334063..0454d5e60e5d 100644
--- a/arch/x86/include/asm/trace/fpu.h
+++ b/arch/x86/include/asm/trace/fpu.h
@@ -74,11 +74,6 @@ DEFINE_EVENT(x86_fpu, x86_fpu_dropped,
 	TP_ARGS(fpu)
 );
 
-DEFINE_EVENT(x86_fpu, x86_fpu_copy_src,
-	TP_PROTO(struct fpu *fpu),
-	TP_ARGS(fpu)
-);
-
 DEFINE_EVENT(x86_fpu, x86_fpu_copy_dst,
 	TP_PROTO(struct fpu *fpu),
 	TP_ARGS(fpu)
-- 
2.25.1.362.g51ebf55


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH tip/x86/fpu 4/6] x86/fpu: arch_dup_task_struct: always use memcpy_and_pad()
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (12 preceding siblings ...)
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 3/6] x86/fpu: kill DEFINE_EVENT(x86_fpu, x86_fpu_copy_src) Oleg Nesterov
@ 2025-05-03 14:38 ` Oleg Nesterov
  2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Always use memcpy_and_pad() in arch_dup_task_struct() tip-bot2 for Oleg Nesterov
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 5/6] x86/fpu: fpu__drop: check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER Oleg Nesterov
  2025-05-03 14:39 ` [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller Oleg Nesterov
  15 siblings, 1 reply; 43+ messages in thread
From: Oleg Nesterov @ 2025-05-03 14:38 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae

It makes no sense to copy the bytes after sizeof(struct task_struct),
FPU state will be initialized in fpu_clone().

A plain memcpy(dst, src, sizeof(struct task_struct)) should work too,
but "_and_pad" looks more safe.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/kernel/process.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7a1bfb61d86f..d01adc028274 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -93,11 +93,9 @@ EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);
  */
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
-	/* init_task is not dynamically sized (incomplete FPU state) */
-	if (unlikely(src == &init_task))
-		memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(init_task), 0);
-	else
-		memcpy(dst, src, arch_task_struct_size);
+	/* fpu_clone() will initialize the "dst_fpu" memory */
+	memcpy_and_pad(dst, arch_task_struct_size, src,
+			sizeof(struct task_struct), 0);
 
 #ifdef CONFIG_VM86
 	dst->thread.vm86 = NULL;
-- 
2.25.1.362.g51ebf55


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH tip/x86/fpu 5/6] x86/fpu: fpu__drop: check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (13 preceding siblings ...)
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 4/6] x86/fpu: arch_dup_task_struct: always use memcpy_and_pad() Oleg Nesterov
@ 2025-05-03 14:38 ` Oleg Nesterov
  2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER in fpu__drop() tip-bot2 for Oleg Nesterov
  2025-05-03 14:39 ` [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller Oleg Nesterov
  15 siblings, 1 reply; 43+ messages in thread
From: Oleg Nesterov @ 2025-05-03 14:38 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae

PF_KTHREAD|PF_USER_WORKER tasks should never clear TIF_NEED_FPU_LOAD,
so the TIF_NEED_FPU_LOAD check should equally filter them out.

And this way an exiting userspace task can avoid the unnecessary "fwait"
if it does context_switch() at least once on its way to exit_thread().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/kernel/fpu/core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 8d674435f173..fa131299c7da 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -693,8 +693,7 @@ void fpu__drop(struct task_struct *tsk)
 {
 	struct fpu *fpu;
 
-	/* PF_KTHREAD tasks do not use the FPU context area: */
-	if (tsk->flags & (PF_KTHREAD | PF_USER_WORKER))
+	if (test_tsk_thread_flag(tsk, TIF_NEED_FPU_LOAD))
 		return;
 
 	fpu = x86_task_fpu(tsk);
-- 
2.25.1.362.g51ebf55


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller
  2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
                   ` (14 preceding siblings ...)
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 5/6] x86/fpu: fpu__drop: check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER Oleg Nesterov
@ 2025-05-03 14:39 ` Oleg Nesterov
  2025-05-04  8:36   ` Ingo Molnar
  2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Shift " tip-bot2 for Oleg Nesterov
  15 siblings, 2 replies; 43+ messages in thread
From: Oleg Nesterov @ 2025-05-03 14:39 UTC (permalink / raw)
  To: Ingo Molnar
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae

If CONFIG_X86_DEBUG_FPU=Y, arch_exit_to_user_mode_prepare() calls
arch_exit_work() even if ti_work == 0. There only reason is that we
want to call fpregs_assert_state_consistent() if TIF_NEED_FPU_LOAD
is not set.

This looks confusing. arch_exit_to_user_mode_prepare() can just call
fpregs_assert_state_consistent() unconditionally, it depends on
CONFIG_X86_DEBUG_FPU and checks TIF_NEED_FPU_LOAD itself.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/include/asm/entry-common.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 77d20555e04d..d535a97c7284 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -53,7 +53,6 @@ static inline void arch_exit_work(unsigned long ti_work)
 	if (unlikely(ti_work & _TIF_IO_BITMAP))
 		tss_update_io_bitmap();
 
-	fpregs_assert_state_consistent();
 	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
 }
@@ -61,7 +60,9 @@ static inline void arch_exit_work(unsigned long ti_work)
 static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 						  unsigned long ti_work)
 {
-	if (IS_ENABLED(CONFIG_X86_DEBUG_FPU) || unlikely(ti_work))
+	fpregs_assert_state_consistent();
+
+	if (unlikely(ti_work))
 		arch_exit_work(ti_work);
 
 	fred_update_rsp0();
-- 
2.25.1.362.g51ebf55


^ permalink raw reply related	[flat|nested] 43+ messages in thread
* Re: [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller
  2025-05-03 14:39 ` [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller Oleg Nesterov
@ 2025-05-04  8:36   ` Ingo Molnar
  2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Shift " tip-bot2 for Oleg Nesterov
  1 sibling, 0 replies; 43+ messages in thread
From: Ingo Molnar @ 2025-05-04  8:36 UTC (permalink / raw)
  To: Oleg Nesterov
  Cc: linux-kernel, Andy Lutomirski, Dave Hansen, Brian Gerst,
	Peter Zijlstra, Borislav Petkov, H . Peter Anvin, Linus Torvalds,
	Thomas Gleixner, Chang S . Bae


* Oleg Nesterov <oleg@redhat.com> wrote:

> If CONFIG_X86_DEBUG_FPU=Y, arch_exit_to_user_mode_prepare() calls
> arch_exit_work() even if ti_work == 0. There only reason is that we
> want to call fpregs_assert_state_consistent() if TIF_NEED_FPU_LOAD
> is not set.
> 
> This looks confusing. arch_exit_to_user_mode_prepare() can just call
> fpregs_assert_state_consistent() unconditionally, it depends on
> CONFIG_X86_DEBUG_FPU and checks TIF_NEED_FPU_LOAD itself.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  arch/x86/include/asm/entry-common.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Thanks Oleg! I've applied these improvements to tip:x86/fpu.

Note that there's still a 32-bit hardened-usercopy regression/crash 
that Boris reported against tip:x86/fpu:

  https://lore.kernel.org/r/20250503120712.GJaBYG8A-D77MllFZ3@fat_crate.local

Which may result in the subsequent rebasing of your commits - but 
otherwise your series looks good to me.

Thanks,

	Ingo

^ permalink raw reply	[flat|nested] 43+ messages in thread
* [tip: x86/fpu] x86/fpu: Shift fpregs_assert_state_consistent() from arch_exit_work() to its caller
  2025-05-03 14:39 ` [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller Oleg Nesterov
  2025-05-04  8:36   ` Ingo Molnar
@ 2025-05-04  8:54   ` tip-bot2 for Oleg Nesterov
  1 sibling, 0 replies; 43+ messages in thread
From: tip-bot2 for Oleg Nesterov @ 2025-05-04  8:54 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Oleg Nesterov, Ingo Molnar, Chang S . Bae, H. Peter Anvin,
	Andy Lutomirski, Brian Gerst, Linus Torvalds, Peter Zijlstra, x86,
	linux-kernel

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     46c158e3ad0fc633007802c338c409c188ec0a12
Gitweb:        https://git.kernel.org/tip/46c158e3ad0fc633007802c338c409c188ec0a12
Author:        Oleg Nesterov <oleg@redhat.com>
AuthorDate:    Sat, 03 May 2025 16:39:02 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 04 May 2025 10:29:25 +02:00

x86/fpu: Shift fpregs_assert_state_consistent() from arch_exit_work() to its caller

If CONFIG_X86_DEBUG_FPU=Y, arch_exit_to_user_mode_prepare() calls
arch_exit_work() even if ti_work == 0. There only reason is that we
want to call fpregs_assert_state_consistent() if TIF_NEED_FPU_LOAD
is not set.

This looks confusing. arch_exit_to_user_mode_prepare() can just call
fpregs_assert_state_consistent() unconditionally, it depends on
CONFIG_X86_DEBUG_FPU and checks TIF_NEED_FPU_LOAD itself.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143902.GA9012@redhat.com
---
 arch/x86/include/asm/entry-common.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 77d2055..d535a97 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -53,7 +53,6 @@ static inline void arch_exit_work(unsigned long ti_work)
 	if (unlikely(ti_work & _TIF_IO_BITMAP))
 		tss_update_io_bitmap();
 
-	fpregs_assert_state_consistent();
 	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
 }
@@ -61,7 +60,9 @@ static inline void arch_exit_work(unsigned long ti_work)
 static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 						  unsigned long ti_work)
 {
-	if (IS_ENABLED(CONFIG_X86_DEBUG_FPU) || unlikely(ti_work))
+	fpregs_assert_state_consistent();
+
+	if (unlikely(ti_work))
 		arch_exit_work(ti_work);
 
 	fred_update_rsp0();

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/fpu] x86/fpu: Check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER in fpu__drop()
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 5/6] x86/fpu: fpu__drop: check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER Oleg Nesterov
@ 2025-05-04  8:54   ` tip-bot2 for Oleg Nesterov
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Oleg Nesterov @ 2025-05-04  8:54 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Oleg Nesterov, Ingo Molnar, Chang S . Bae, H. Peter Anvin,
	Andy Lutomirski, Brian Gerst, Linus Torvalds, Peter Zijlstra, x86,
	linux-kernel

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     016a2e6f8ae5ed544ba8fb2b6d78f64ddfd9d01b
Gitweb:        https://git.kernel.org/tip/016a2e6f8ae5ed544ba8fb2b6d78f64ddfd9d01b
Author:        Oleg Nesterov <oleg@redhat.com>
AuthorDate:    Sat, 03 May 2025 16:38:56 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 04 May 2025 10:29:25 +02:00

x86/fpu: Check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER in fpu__drop()

PF_KTHREAD|PF_USER_WORKER tasks should never clear TIF_NEED_FPU_LOAD,
so the TIF_NEED_FPU_LOAD check should equally filter them out.

And this way an exiting userspace task can avoid the unnecessary "fwait"
if it does context_switch() at least once on its way to exit_thread().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143856.GA9009@redhat.com
---
 arch/x86/kernel/fpu/core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 8d67443..fa13129 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -693,8 +693,7 @@ void fpu__drop(struct task_struct *tsk)
 {
 	struct fpu *fpu;
 
-	/* PF_KTHREAD tasks do not use the FPU context area: */
-	if (tsk->flags & (PF_KTHREAD | PF_USER_WORKER))
+	if (test_tsk_thread_flag(tsk, TIF_NEED_FPU_LOAD))
 		return;
 
 	fpu = x86_task_fpu(tsk);

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/fpu] x86/fpu: Always use memcpy_and_pad() in arch_dup_task_struct()
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 4/6] x86/fpu: arch_dup_task_struct: always use memcpy_and_pad() Oleg Nesterov
@ 2025-05-04  8:54   ` tip-bot2 for Oleg Nesterov
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Oleg Nesterov @ 2025-05-04  8:54 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Oleg Nesterov, Ingo Molnar, Andy Lutomirski, Brian Gerst,
	Chang S . Bae, H. Peter Anvin, Linus Torvalds, Peter Zijlstra,
	x86, linux-kernel

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     2d299e3d773d519ee93e5aaa3ffddd4a6276b005
Gitweb:        https://git.kernel.org/tip/2d299e3d773d519ee93e5aaa3ffddd4a6276b005
Author:        Oleg Nesterov <oleg@redhat.com>
AuthorDate:    Sat, 03 May 2025 16:38:50 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 04 May 2025 10:29:25 +02:00

x86/fpu: Always use memcpy_and_pad() in arch_dup_task_struct()

It makes no sense to copy the bytes after sizeof(struct task_struct),
FPU state will be initialized in fpu_clone().

A plain memcpy(dst, src, sizeof(struct task_struct)) should work too,
but "_and_pad" looks safer.

[ mingo: Simplify it a bit more. ]

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143850.GA8997@redhat.com
---
 arch/x86/kernel/process.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7a1bfb6..9e61807 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -93,11 +93,8 @@ EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);
  */
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
-	/* init_task is not dynamically sized (incomplete FPU state) */
-	if (unlikely(src == &init_task))
-		memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(init_task), 0);
-	else
-		memcpy(dst, src, arch_task_struct_size);
+	/* fpu_clone() will initialize the "dst_fpu" memory */
+	memcpy_and_pad(dst, arch_task_struct_size, src, sizeof(*dst), 0);
 
 #ifdef CONFIG_VM86
 	dst->thread.vm86 = NULL;

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/fpu] x86/fpu: Remove DEFINE_EVENT(x86_fpu, x86_fpu_copy_src)
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 3/6] x86/fpu: kill DEFINE_EVENT(x86_fpu, x86_fpu_copy_src) Oleg Nesterov
@ 2025-05-04  8:54   ` tip-bot2 for Oleg Nesterov
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Oleg Nesterov @ 2025-05-04  8:54 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Oleg Nesterov, Ingo Molnar, Chang S . Bae, H. Peter Anvin,
	Andy Lutomirski, Brian Gerst, Linus Torvalds, Peter Zijlstra, x86,
	linux-kernel

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     8e269c030ecafbfebf4f55e24fb336fd7b489708
Gitweb:        https://git.kernel.org/tip/8e269c030ecafbfebf4f55e24fb336fd7b489708
Author:        Oleg Nesterov <oleg@redhat.com>
AuthorDate:    Sat, 03 May 2025 16:38:43 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 04 May 2025 10:29:25 +02:00

x86/fpu: Remove DEFINE_EVENT(x86_fpu, x86_fpu_copy_src)

trace_x86_fpu_copy_src() has no users after:

  22aafe3bcb67 ("x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks")

Remove the event.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143843.GA8989@redhat.com
---
 arch/x86/include/asm/trace/fpu.h | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/arch/x86/include/asm/trace/fpu.h b/arch/x86/include/asm/trace/fpu.h
index 4645a63..0454d5e 100644
--- a/arch/x86/include/asm/trace/fpu.h
+++ b/arch/x86/include/asm/trace/fpu.h
@@ -74,11 +74,6 @@ DEFINE_EVENT(x86_fpu, x86_fpu_dropped,
 	TP_ARGS(fpu)
 );
 
-DEFINE_EVENT(x86_fpu, x86_fpu_copy_src,
-	TP_PROTO(struct fpu *fpu),
-	TP_ARGS(fpu)
-);
-
 DEFINE_EVENT(x86_fpu, x86_fpu_copy_dst,
 	TP_PROTO(struct fpu *fpu),
 	TP_ARGS(fpu)

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/fpu] x86/fpu: Remove x86_init_fpu
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 2/6] x86/fpu: kill x86_init_fpu Oleg Nesterov
@ 2025-05-04  8:54   ` tip-bot2 for Oleg Nesterov
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Oleg Nesterov @ 2025-05-04  8:54 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Oleg Nesterov, Ingo Molnar, Chang S . Bae, H. Peter Anvin,
	Andy Lutomirski, Brian Gerst, Linus Torvalds, Peter Zijlstra, x86,
	linux-kernel

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     392bbe11c7cf90e65cba32e90af3b969a981c4fe
Gitweb:        https://git.kernel.org/tip/392bbe11c7cf90e65cba32e90af3b969a981c4fe
Author:        Oleg Nesterov <oleg@redhat.com>
AuthorDate:    Sat, 03 May 2025 16:38:37 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 04 May 2025 10:29:24 +02:00

x86/fpu: Remove x86_init_fpu

It is not actually used after:

  55bc30f2e34d ("x86/fpu: Remove the thread::fpu pointer")

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143837.GA8985@redhat.com
---
 arch/x86/kernel/fpu/init.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 2d9b5e6..6bb3e35 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -71,13 +71,9 @@ static bool __init fpu__probe_without_cpuid(void)
 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
 }
 
-static struct fpu x86_init_fpu __attribute__ ((aligned (64))) __read_mostly;
-
 static void __init fpu__init_system_early_generic(void)
 {
-	fpstate_reset(&x86_init_fpu);
 	set_thread_flag(TIF_NEED_FPU_LOAD);
-	x86_init_fpu.last_cpu = -1;
 
 	if (!boot_cpu_has(X86_FEATURE_CPUID) &&
 	    !test_bit(X86_FEATURE_FPU, (unsigned long *)cpu_caps_cleared)) {

^ permalink raw reply related	[flat|nested] 43+ messages in thread
* [tip: x86/fpu] x86/fpu: Simplify the switch_fpu_prepare() + switch_fpu_finish() logic
  2025-05-03 14:38 ` [PATCH tip/x86/fpu 1/6] x86/fpu: simplify the switch_fpu_prepare() + switch_fpu_finish() logic Oleg Nesterov
@ 2025-05-04  8:54   ` tip-bot2 for Oleg Nesterov
  0 siblings, 0 replies; 43+ messages in thread
From: tip-bot2 for Oleg Nesterov @ 2025-05-04  8:54 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Oleg Nesterov, Ingo Molnar, Chang S . Bae, H. Peter Anvin,
	Andy Lutomirski, Brian Gerst, Linus Torvalds, Peter Zijlstra, x86,
	linux-kernel

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     730faa15a069f4025a0f8c2a5244c3067da7ecbe
Gitweb:        https://git.kernel.org/tip/730faa15a069f4025a0f8c2a5244c3067da7ecbe
Author:        Oleg Nesterov <oleg@redhat.com>
AuthorDate:    Sat, 03 May 2025 16:38:30 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 04 May 2025 10:29:24 +02:00

x86/fpu: Simplify the switch_fpu_prepare() + switch_fpu_finish() logic

Now that switch_fpu_finish() doesn't load the FPU state, it makes more
sense to fold it into switch_fpu_prepare() renamed to switch_fpu(), and
more importantly, use the "prev_p" task as a target for TIF_NEED_FPU_LOAD.
It doesn't make any sense to delay set_tsk_thread_flag(TIF_NEED_FPU_LOAD)
until "prev_p" is scheduled again.

There is no worry about the very first context switch, fpu_clone() must
always set TIF_NEED_FPU_LOAD.

Also, shift the test_tsk_thread_flag(TIF_NEED_FPU_LOAD) from the callers
to switch_fpu().

Note that the "PF_KTHREAD | PF_USER_WORKER" check can be removed but
this deserves a separate patch which can change more functions, say,
kernel_fpu_begin_mask().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143830.GA8982@redhat.com
---
 arch/x86/include/asm/fpu/sched.h | 34 ++++++++-----------------------
 arch/x86/kernel/process_32.c     |  5 +----
 arch/x86/kernel/process_64.c     |  5 +----
 3 files changed, 11 insertions(+), 33 deletions(-)

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index 5fd1263..c060549 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -18,31 +18,25 @@ extern void fpu_flush_thread(void);
 /*
  * FPU state switching for scheduling.
  *
- * This is a two-stage process:
+ * switch_fpu() saves the old state and sets TIF_NEED_FPU_LOAD if
+ * TIF_NEED_FPU_LOAD is not set.  This is done within the context
+ * of the old process.
  *
- *  - switch_fpu_prepare() saves the old state.
- *    This is done within the context of the old process.
- *
- *  - switch_fpu_finish() sets TIF_NEED_FPU_LOAD; the floating point state
- *    will get loaded on return to userspace, or when the kernel needs it.
- *
- * If TIF_NEED_FPU_LOAD is cleared then the CPU's FPU registers
- * are saved in the current thread's FPU register state.
- *
- * If TIF_NEED_FPU_LOAD is set then CPU's FPU registers may not
- * hold current()'s FPU registers. It is required to load the
+ * Once TIF_NEED_FPU_LOAD is set, it is required to load the
  * registers before returning to userland or using the content
  * otherwise.
  *
  * The FPU context is only stored/restored for a user task and
  * PF_KTHREAD is used to distinguish between kernel and user threads.
  */
-static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
+static inline void switch_fpu(struct task_struct *old, int cpu)
 {
-	if (cpu_feature_enabled(X86_FEATURE_FPU) &&
+	if (!test_tsk_thread_flag(old, TIF_NEED_FPU_LOAD) &&
+	    cpu_feature_enabled(X86_FEATURE_FPU) &&
 	    !(old->flags & (PF_KTHREAD | PF_USER_WORKER))) {
 		struct fpu *old_fpu = x86_task_fpu(old);
 
+		set_tsk_thread_flag(old, TIF_NEED_FPU_LOAD);
 		save_fpregs_to_fpstate(old_fpu);
 		/*
 		 * The save operation preserved register state, so the
@@ -50,7 +44,7 @@ static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
 		 * current CPU number in @old_fpu, so the next return
 		 * to user space can avoid the FPU register restore
 		 * when is returns on the same CPU and still owns the
-		 * context.
+		 * context. See fpregs_restore_userregs().
 		 */
 		old_fpu->last_cpu = cpu;
 
@@ -58,14 +52,4 @@ static inline void switch_fpu_prepare(struct task_struct *old, int cpu)
 	}
 }
 
-/*
- * Delay loading of the complete FPU state until the return to userland.
- * PKRU is handled separately.
- */
-static inline void switch_fpu_finish(struct task_struct *new)
-{
-	if (cpu_feature_enabled(X86_FEATURE_FPU))
-		set_tsk_thread_flag(new, TIF_NEED_FPU_LOAD);
-}
-
 #endif /* _ASM_X86_FPU_SCHED_H */
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 4636ef3..9bd4fa6 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -160,8 +160,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 
 	/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
 
-	if (!test_tsk_thread_flag(prev_p, TIF_NEED_FPU_LOAD))
-		switch_fpu_prepare(prev_p, cpu);
+	switch_fpu(prev_p, cpu);
 
 	/*
 	 * Save away %gs. No need to save %fs, as it was saved on the
@@ -208,8 +207,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 
 	raw_cpu_write(current_task, next_p);
 
-	switch_fpu_finish(next_p);
-
 	/* Load the Intel cache allocation PQR MSR. */
 	resctrl_sched_in(next_p);
 
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 7196ca7..d55310d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -616,8 +616,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ENTRY) &&
 		     this_cpu_read(hardirq_stack_inuse));
 
-	if (!test_tsk_thread_flag(prev_p, TIF_NEED_FPU_LOAD))
-		switch_fpu_prepare(prev_p, cpu);
+	switch_fpu(prev_p, cpu);
 
 	/* We must save %fs and %gs before load_TLS() because
 	 * %fs and %gs may be cleared by load_TLS().
@@ -671,8 +670,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	raw_cpu_write(current_task, next_p);
 	raw_cpu_write(cpu_current_top_of_stack, task_top_of_stack(next_p));
 
-	switch_fpu_finish(next_p);
-
 	/* Reload sp0. */
 	update_task_stack(next_p);
 

^ permalink raw reply related	[flat|nested] 43+ messages in thread
end of thread, other threads:[~2025-05-04  8:54 UTC | newest]

Thread overview: 43+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-04-09 21:11 [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Ingo Molnar
2025-04-09 21:11 ` [PATCH 1/8] x86/fpu: Introduce the x86_task_fpu() helper method Ingo Molnar
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-09 21:11 ` [PATCH 2/8] x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu() Ingo Molnar
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-09 21:11 ` [PATCH 3/8] x86/fpu: Make task_struct::thread constant size Ingo Molnar
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-09 21:11 ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
2025-04-10  7:39   ` Peter Zijlstra
2025-04-10 10:10     ` Ingo Molnar
2025-04-10 10:30       ` Peter Zijlstra
2025-04-10 10:54         ` [PATCH] x86/fpu: Clarify FPU context cacheline alignment Ingo Molnar
2025-04-14  7:34           ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-10 10:51       ` [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer Ingo Molnar
2025-04-10 14:04       ` Oleg Nesterov
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-09 21:11 ` [PATCH 5/8] x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call Ingo Molnar
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-09 21:11 ` [PATCH 6/8] x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit Ingo Molnar
2025-04-11 15:22   ` Chang S. Bae
2025-04-12  8:37     ` Ingo Molnar
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-09 21:11 ` [PATCH 7/8] x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks Ingo Molnar
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-09 21:11 ` [PATCH 8/8] x86/fpu: Use 'fpstate' variable names consistently Ingo Molnar
2025-04-14  7:34   ` [tip: x86/merge] " tip-bot2 for Ingo Molnar
2025-04-22 16:11 ` [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu Oleg Nesterov
2025-04-22 20:09   ` Ingo Molnar
2025-04-22 17:01 ` question about switch_fpu_prepare/switch_fpu_finish Oleg Nesterov
2025-04-22 20:11   ` Ingo Molnar
2025-05-03 14:38 ` [PATCH tip/x86/fpu 1/6] x86/fpu: simplify the switch_fpu_prepare() + switch_fpu_finish() logic Oleg Nesterov
2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Simplify " tip-bot2 for Oleg Nesterov
2025-05-03 14:38 ` [PATCH tip/x86/fpu 2/6] x86/fpu: kill x86_init_fpu Oleg Nesterov
2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Remove x86_init_fpu tip-bot2 for Oleg Nesterov
2025-05-03 14:38 ` [PATCH tip/x86/fpu 3/6] x86/fpu: kill DEFINE_EVENT(x86_fpu, x86_fpu_copy_src) Oleg Nesterov
2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Remove " tip-bot2 for Oleg Nesterov
2025-05-03 14:38 ` [PATCH tip/x86/fpu 4/6] x86/fpu: arch_dup_task_struct: always use memcpy_and_pad() Oleg Nesterov
2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Always use memcpy_and_pad() in arch_dup_task_struct() tip-bot2 for Oleg Nesterov
2025-05-03 14:38 ` [PATCH tip/x86/fpu 5/6] x86/fpu: fpu__drop: check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER Oleg Nesterov
2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Check TIF_NEED_FPU_LOAD instead of PF_KTHREAD|PF_USER_WORKER in fpu__drop() tip-bot2 for Oleg Nesterov
2025-05-03 14:39 ` [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller Oleg Nesterov
2025-05-04  8:36   ` Ingo Molnar
2025-05-04  8:54   ` [tip: x86/fpu] x86/fpu: Shift " tip-bot2 for Oleg Nesterov

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