linux-kernel - [RFC PATCH 16/22] x86/fpu/xstate: Support dynamic user state in the signal handling path

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Date:   Thu,  1 Oct 2020 13:39:07 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     tglx@...utronix.de, mingo@...nel.org, bp@...e.de, luto@...nel.org,
        x86@...nel.org
Cc:     len.brown@...el.com, dave.hansen@...el.com, jing2.liu@...el.com,
        ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org,
        chang.seok.bae@...el.com
Subject: [RFC PATCH 16/22] x86/fpu/xstate: Support dynamic user state in the signal handling path

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

Returning from signal handler, XRSTOR re-initializes the excluded state
components.

No functional change until the kernel actually supports the dynamic user
states.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
---
 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 f5dbbaa060fb..fd044b31ce40 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -368,7 +368,7 @@ 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