[PATCH 12/13] x86/boot: Don't overwrite cr4 when enabling PAE

Matt Fleming
2014-03-04T13:16:00Z

Some EFI firmware makes use of the FPU during boottime services and
clearing X86_CR4_OSFXSR by overwriting %cr4 causes the firmware to
crash.

Add the PAE bit explicitly instead of trashing the existing contents,
leaving the rest of the bits as the firmware set them.

Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
---
arch/x86/boot/compressed/head_64.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 37c741b0d2ac..4f40cddd025d 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -113,7 +113,8 @@ ENTRY(startup_32)
lgdt gdt(%ebp)

/* Enable PAE mode */
- movl $(X86_CR4_PAE), %eax
+ movl %cr4, %eax
+ orl $X86_CR4_PAE, %eax
movl %eax, %cr4

/*
--
1.8.5.3