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Subject[PATCH 2/4] x86/mmx: Use KFPU_MMX for MMX string operations
Date
The default kernel_fpu_begin() doesn't work on systems that support XMM but
haven't yet enabled OSFXSR. This causes crashes when _mmx_memcpy() is
called too early.

Fix it by using kernel_fpu_begin(KFPU_MMX) explicitly. This should also be
faster, since it skips both the reasonably fast LDMXCSR and also the rather
slow FNINIT instructions.

Fixes: 7ad816762f9b ("x86/fpu: Reset MXCSR to default in kernel_fpu_begin()")
Reported-by: Krzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/lib/mmx_32.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/lib/mmx_32.c b/arch/x86/lib/mmx_32.c
index 4321fa02e18d..daa80fa005fb 100644
--- a/arch/x86/lib/mmx_32.c
+++ b/arch/x86/lib/mmx_32.c
@@ -37,7 +37,7 @@ void *_mmx_memcpy(void *to, const void *from, size_t len)
p = to;
i = len >> 6; /* len/64 */

- kernel_fpu_begin();
+ kernel_fpu_begin_mask(KFPU_MMX);

__asm__ __volatile__ (
"1: prefetch (%0)\n" /* This set is 28 bytes */
@@ -127,7 +127,7 @@ static void fast_clear_page(void *page)
{
int i;

- kernel_fpu_begin();
+ kernel_fpu_begin_mask(KFPU_MMX);

__asm__ __volatile__ (
" pxor %%mm0, %%mm0\n" : :
@@ -160,7 +160,7 @@ static void fast_copy_page(void *to, void *from)
{
int i;

- kernel_fpu_begin();
+ kernel_fpu_begin_mask(KFPU_MMX);

/*
* maybe the prefetch stuff can go before the expensive fnsave...
@@ -247,7 +247,7 @@ static void fast_clear_page(void *page)
{
int i;

- kernel_fpu_begin();
+ kernel_fpu_begin_mask(KFPU_MMX);

__asm__ __volatile__ (
" pxor %%mm0, %%mm0\n" : :
@@ -282,7 +282,7 @@ static void fast_copy_page(void *to, void *from)
{
int i;

- kernel_fpu_begin();
+ kernel_fpu_begin_mask(KFPU_MMX);

__asm__ __volatile__ (
"1: prefetch (%0)\n"
--
2.29.2
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