[PATCH v5 24/28] x86/fpu/xstate: Use per-task xstate mask for saving xstate in signal frame

[Chang S. Bae]

Entering a signal handler, the kernel saves xstate in signal frame. The
dynamic user state is better to be saved only when used. fpu->state_mask
can help to exclude unused states.

Returning from a signal handler, XRSTOR(S) re-initializes the excluded
state components.

Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Reviewed-by: Len Brown <len.brown@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
Changes from v4:
* Updated the title and the changelog.
* Excluded the test case addition; separated out as a new patch.

Changes from v3:
* Removed 'no functional changes' in the changelog. (Borislav Petkov)

Changes from v1:
* Made it revertable (moved close to the end of the series).
* Included the test case.
---
 arch/x86/include/asm/fpu/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 6460d52991ba..4a3436684805 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -354,7 +354,7 @@ static inline void copy_kernel_to_xregs(struct xregs_state *xstate, u64 mask)
  */
 static inline int copy_xregs_to_user(struct xregs_state __user *buf)
 {
-	u64 mask = xfeatures_mask_user();
+	u64 mask = current->thread.fpu.state_mask;
 	u32 lmask = mask;
 	u32 hmask = mask >> 32;
 	int err;
-- 
2.17.1