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

[Matt Fleming]

From: Matt Fleming <matt.fleming@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Matt Fleming <matt.fleming@xxxxxxxxx>
---
 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

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