From 8e221b6db4477643fefc885a97ea9889ac733140 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Tue, 22 Jun 2010 16:23:37 -0700 Subject: x86: Avoid unnecessary __clear_user() and xrstor in signal handling fxsave/xsave doesn't touch all the bytes in the memory layout used by these instructions. Specifically SW reserved (bytes 464..511) fields in the fxsave frame and the reserved fields in the xsave header. To present a clean context for the signal handling, just clear these fields instead of clearing the complete fxsave/xsave memory layout, when we dump these registers directly to the user signal frame. Also avoid the call to second xrstor (which inits the state not passed in the signal frame) in restore_user_xstate() if all the state has already been restored by the first xrstor. These changes improve the performance of signal handling(by ~3-5% as measured by the lat_sig). Signed-off-by: Suresh Siddha LKML-Reference: <1277249017.2847.85.camel@sbs-t61.sc.intel.com> Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/i387.h | 9 +++++++++ arch/x86/include/asm/xsave.h | 10 ++++++++++ 2 files changed, 19 insertions(+) (limited to 'arch/x86/include/asm') diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h index c991b3a7b904..0f1cf5d53dd8 100644 --- a/arch/x86/include/asm/i387.h +++ b/arch/x86/include/asm/i387.h @@ -127,6 +127,15 @@ static inline int fxsave_user(struct i387_fxsave_struct __user *fx) { int err; + /* + * Clear the bytes not touched by the fxsave and reserved + * for the SW usage. + */ + err = __clear_user(&fx->sw_reserved, + sizeof(struct _fpx_sw_bytes)); + if (unlikely(err)) + return -EFAULT; + asm volatile("1: rex64/fxsave (%[fx])\n\t" "2:\n" ".section .fixup,\"ax\"\n" diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h index 2c4390cae228..30dfc81804d5 100644 --- a/arch/x86/include/asm/xsave.h +++ b/arch/x86/include/asm/xsave.h @@ -59,6 +59,16 @@ static inline int fpu_xrstor_checking(struct fpu *fpu) static inline int xsave_user(struct xsave_struct __user *buf) { int err; + + /* + * Clear the xsave header first, so that reserved fields are + * initialized to zero. + */ + err = __clear_user(&buf->xsave_hdr, + sizeof(struct xsave_hdr_struct)); + if (unlikely(err)) + return -EFAULT; + __asm__ __volatile__("1: .byte " REX_PREFIX "0x0f,0xae,0x27\n" "2:\n" ".section .fixup,\"ax\"\n" -- cgit v1.2.2