[PATCH v9 09/26] x86/fpu/xstate: Update the XSTATE save function to support dynamic states

Chang S. Bae
2021-07-30T15:06:25Z

Extend os_xsave() to receive a mask argument of which states to save, in
preparation for dynamic user state handling.

Update KVM to set a valid fpu->state_mask, so it can continue to share with
the core code.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kvm@vger.kernel.org
---
Changes from v5:
* Adjusted the changelog and code for the new base code.

Changes from v3:
* Updated the changelog. (Borislav Petkov)
* Made the code change more reviewable.

Changes from v2:
* Updated the changelog to clarify the KVM code changes.
---
arch/x86/include/asm/fpu/internal.h | 3 +--
arch/x86/kernel/fpu/core.c | 2 +-
arch/x86/kernel/fpu/signal.c | 2 +-
arch/x86/kvm/x86.c | 9 +++++++--
4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index d2fc19c0e457..263e349ff85a 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -298,9 +298,8 @@ static inline void os_xrstor_booting(struct xregs_state *xstate)
* Uses either XSAVE or XSAVEOPT or XSAVES depending on the CPU features
* and command line options. The choice is permanent until the next reboot.
*/
-static inline void os_xsave(struct xregs_state *xstate)
+static inline void os_xsave(struct xregs_state *xstate, u64 mask)
{
- u64 mask = xfeatures_mask_all;
u32 lmask = mask;
u32 hmask = mask >> 32;
int err;
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 16abc0357e2e..541628bfc8c0 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -99,7 +99,7 @@ EXPORT_SYMBOL(irq_fpu_usable);
void save_fpregs_to_fpstate(struct fpu *fpu)
{
if (likely(use_xsave())) {
- os_xsave(&fpu->state->xsave);
+ os_xsave(&fpu->state->xsave, fpu->state_mask);

/*
* AVX512 state is tracked here because its use is
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 2f35aada2007..f70f84d53442 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -365,7 +365,7 @@ static int __fpu_restore_sig(void __user *buf, void __user *buf_fx,
* the right place in memory. It's ia32 mode. Shrug.
*/
if (xfeatures_mask_supervisor())
- os_xsave(&fpu->state->xsave);
+ os_xsave(&fpu->state->xsave, fpu->state_mask);
set_thread_flag(TIF_NEED_FPU_LOAD);
}
__fpu_invalidate_fpregs_state(fpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 18a337f99459..97b68c6cacd2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9890,11 +9890,16 @@ static void kvm_save_current_fpu(struct fpu *fpu)
* KVM does not support dynamic user states yet. Assume the buffer
* always has the minimum size.
*/
- if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ if (test_thread_flag(TIF_NEED_FPU_LOAD)) {
memcpy(fpu->state, current->thread.fpu.state,
get_xstate_config(XSTATE_MIN_SIZE));
- else
+ } else {
+ struct fpu *src_fpu = &current->thread.fpu;
+
+ if (fpu->state_mask != src_fpu->state_mask)
+ fpu->state_mask = src_fpu->state_mask;
save_fpregs_to_fpstate(fpu);
+ }
}

/* Swap (qemu) user FPU context for the guest FPU context. */
--
2.17.1