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From: H. Peter Anvin on 6 Aug 2010 19:10
Hi Linus,

The following changes since commit fc1caf6eafb30ea185720e29f7f5eccca61ecd60:

Merge branch 'drm-core-next' of git://git.kernel.org/pub/scm/linux/kernel/git/airlied/drm-2.6 (2010-08-05 16:02:01 -0700)

are available in the git repository at:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git x86-fpu-for-linus

Suresh Siddha (1):
x86: Avoid unnecessary __clear_user() and xrstor in signal handling

arch/x86/include/asm/i387.h | 9 +++++++++
arch/x86/include/asm/xsave.h | 10 ++++++++++
arch/x86/kernel/xsave.c | 12 ++----------
3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index 815c5b2..f1accc6 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 32c3666..06acdbd 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -65,6 +65,16 @@ 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"
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 37e68fc..6e73db1 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -91,14 +91,6 @@ int save_i387_xstate(void __user *buf)
return 0;

if (task_thread_info(tsk)->status & TS_USEDFPU) {
- /*
- * Start with clearing the user buffer. This will present a
- * clean context for the bytes not touched by the fxsave/xsave.
- */
- err = __clear_user(buf, sig_xstate_size);
- if (err)
- return err;
-
if (use_xsave())
err = xsave_user(buf);
else
@@ -184,8 +176,8 @@ static int restore_user_xstate(void __user *buf)
* init the state skipped by the user.
*/
mask = pcntxt_mask & ~mask;
-
- xrstor_state(init_xstate_buf, mask);
+ if (unlikely(mask))
+ xrstor_state(init_xstate_buf, mask);

return 0;

--
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