[patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

Thomas Gleixner
2021-10-12T00:06:37Z

Swapping the host/guest FPU is directly fiddling with FPU internals which
requires 5 exports. The upcoming support of dymanically enabled states
would even need more.

Implement a swap function in the FPU core code and export that instead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/include/asm/fpu/api.h | 8 +++++
arch/x86/include/asm/fpu/internal.h | 15 +---------
arch/x86/kernel/fpu/core.c | 30 ++++++++++++++++++---
arch/x86/kernel/fpu/init.c | 1
arch/x86/kernel/fpu/xstate.c | 1
arch/x86/kvm/x86.c | 51 +++++++-----------------------------
arch/x86/mm/extable.c | 2 -
7 files changed, 48 insertions(+), 60 deletions(-)

--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -12,6 +12,8 @@
#define _ASM_X86_FPU_API_H
#include <linux/bottom_half.h>

+#include <asm/fpu/types.h>
+
/*
* Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It
* disables preemption so be careful if you intend to use it for long periods
@@ -108,4 +110,10 @@ extern int cpu_has_xfeatures(u64 xfeatur

static inline void update_pasid(void) { }

+/* FPSTATE related functions which are exported to KVM */
+extern void fpu_init_fpstate_user(struct fpu *fpu);
+
+/* KVM specific functions */
+extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
+
#endif /* _ASM_X86_FPU_API_H */
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -74,14 +74,8 @@ static __always_inline __pure bool use_f
return static_cpu_has(X86_FEATURE_FXSR);
}

-/*
- * fpstate handling functions:
- */
-
extern union fpregs_state init_fpstate;
-
extern void fpstate_init_user(union fpregs_state *state);
-extern void fpu_init_fpstate_user(struct fpu *fpu);

#ifdef CONFIG_MATH_EMULATION
extern void fpstate_init_soft(struct swregs_state *soft);
@@ -381,12 +375,7 @@ static inline int os_xrstor_safe(struct
return err;
}

-extern void __restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask);
-
-static inline void restore_fpregs_from_fpstate(union fpregs_state *fpstate)
-{
- __restore_fpregs_from_fpstate(fpstate, xfeatures_mask_fpstate());
-}
+extern void restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask);

extern bool copy_fpstate_to_sigframe(void __user *buf, void __user *fp, int size);

@@ -467,7 +456,7 @@ static inline void fpregs_restore_userre
*/
mask = xfeatures_mask_restore_user() |
xfeatures_mask_supervisor();
- __restore_fpregs_from_fpstate(&fpu->state, mask);
+ restore_fpregs_from_fpstate(&fpu->state, mask);

fpregs_activate(fpu);
fpu->last_cpu = cpu;
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -124,9 +124,8 @@ void save_fpregs_to_fpstate(struct fpu *
asm volatile("fnsave %[fp]; fwait" : [fp] "=m" (fpu->state.fsave));
frstor(&fpu->state.fsave);
}
-EXPORT_SYMBOL(save_fpregs_to_fpstate);

-void __restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask)
+void restore_fpregs_from_fpstate(union fpregs_state *fpstate, u64 mask)
{
/*
* AMD K7/K8 and later CPUs up to Zen don't save/restore
@@ -151,7 +150,31 @@ void __restore_fpregs_from_fpstate(union
frstor(&fpstate->fsave);
}
}
-EXPORT_SYMBOL_GPL(__restore_fpregs_from_fpstate);
+
+#if IS_ENABLED(CONFIG_KVM)
+void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
+{
+ fpregs_lock();
+
+ if (save) {
+ if (test_thread_flag(TIF_NEED_FPU_LOAD)) {
+ memcpy(&save->state, &current->thread.fpu.state,
+ fpu_kernel_xstate_size);
+ } else {
+ save_fpregs_to_fpstate(save);
+ }
+ }
+
+ if (rstor) {
+ restore_mask &= xfeatures_mask_fpstate();
+ restore_fpregs_from_fpstate(&rstor->state, restore_mask);
+ }
+
+ fpregs_mark_activate();
+ fpregs_unlock();
+}
+EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpu);
+#endif

void kernel_fpu_begin_mask(unsigned int kfpu_mask)
{
@@ -459,7 +482,6 @@ void fpregs_mark_activate(void)
fpu->last_cpu = smp_processor_id();
clear_thread_flag(TIF_NEED_FPU_LOAD);
}
-EXPORT_SYMBOL_GPL(fpregs_mark_activate);

/*
* x87 math exception handling:
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -136,7 +136,6 @@ static void __init fpu__init_system_gene
* components into a single, continuous memory block:
*/
unsigned int fpu_kernel_xstate_size __ro_after_init;
-EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);

/* Get alignment of the TYPE. */
#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -65,7 +65,6 @@ static short xsave_cpuid_features[] __in
* XSAVE buffer, both supervisor and user xstates.
*/
u64 xfeatures_mask_all __ro_after_init;
-EXPORT_SYMBOL_GPL(xfeatures_mask_all);

static unsigned int xstate_offsets[XFEATURE_MAX] __ro_after_init =
{ [ 0 ... XFEATURE_MAX - 1] = -1};
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -68,7 +68,9 @@
#include <asm/mce.h>
#include <asm/pkru.h>
#include <linux/kernel_stat.h>
-#include <asm/fpu/internal.h> /* Ugh! */
+#include <asm/fpu/api.h>
+#include <asm/fpu/xcr.h>
+#include <asm/fpu/xstate.h>
#include <asm/pvclock.h>
#include <asm/div64.h>
#include <asm/irq_remapping.h>
@@ -9899,58 +9901,27 @@ static int complete_emulated_mmio(struct
return 0;
}

-static void kvm_save_current_fpu(struct fpu *fpu)
-{
- /*
- * If the target FPU state is not resident in the CPU registers, just
- * memcpy() from current, else save CPU state directly to the target.
- */
- if (test_thread_flag(TIF_NEED_FPU_LOAD))
- memcpy(&fpu->state, &current->thread.fpu.state,
- fpu_kernel_xstate_size);
- else
- save_fpregs_to_fpstate(fpu);
-}
-
/* Swap (qemu) user FPU context for the guest FPU context. */
static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
{
- fpregs_lock();
-
- kvm_save_current_fpu(vcpu->arch.user_fpu);
-
/*
- * Guests with protected state can't have it set by the hypervisor,
- * so skip trying to set it.
+ * Guest with protected state have guest_fpu == NULL which makes
+ * the swap only safe the host state. Exclude PKRU from restore as
+ * it is restored separately in kvm_x86_ops.run().
*/
- if (vcpu->arch.guest_fpu)
- /* PKRU is separately restored in kvm_x86_ops.run. */
- __restore_fpregs_from_fpstate(&vcpu->arch.guest_fpu->state,
- ~XFEATURE_MASK_PKRU);
-
- fpregs_mark_activate();
- fpregs_unlock();
-
+ fpu_swap_kvm_fpu(vcpu->arch.user_fpu, vcpu->arch.guest_fpu,
+ ~XFEATURE_MASK_PKRU);
trace_kvm_fpu(1);
}

/* When vcpu_run ends, restore user space FPU context. */
static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
{
- fpregs_lock();
-
/*
- * Guests with protected state can't have it read by the hypervisor,
- * so skip trying to save it.
+ * Guest with protected state have guest_fpu == NULL which makes
+ * swap only restore the host state.
*/
- if (vcpu->arch.guest_fpu)
- kvm_save_current_fpu(vcpu->arch.guest_fpu);
-
- restore_fpregs_from_fpstate(&vcpu->arch.user_fpu->state);
-
- fpregs_mark_activate();
- fpregs_unlock();
-
+ fpu_swap_kvm_fpu(vcpu->arch.guest_fpu, vcpu->arch.user_fpu, ~0ULL);
++vcpu->stat.fpu_reload;
trace_kvm_fpu(0);
}
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -47,7 +47,7 @@ static bool ex_handler_fprestore(const s
WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
(void *)instruction_pointer(regs));

- __restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
+ restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
return true;
}