[Xen-devel] [PATCH 2/2] x86/msr: Set the return value to zero when native_rdmsr_safe fails

[Andy Lutomirski <luto@xxxxxxxxxx>]

This will cause unchecked native_rdmsr_safe failures to return
deterministic results.

We could poison the results with something other than zero, but that
would increase code size.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/include/asm/msr.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 77d8b284e4a7..9eda52205d42 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -73,7 +73,10 @@ static inline unsigned long long 
native_read_msr_safe(unsigned int msr,
        asm volatile("2: rdmsr ; xor %[err],%[err]\n"
                     "1:\n\t"
                     ".section .fixup,\"ax\"\n\t"
-                    "3:  mov %[fault],%[err] ; jmp 1b\n\t"
+                    "3: mov %[fault],%[err]\n\t"
+                    "xorl %%eax, %%eax\n\t"
+                    "xorl %%edx, %%edx\n\t"
+                    "jmp 1b\n\t"
                     ".previous\n\t"
                     _ASM_EXTABLE(2b, 3b)
                     : [err] "=r" (*err), EAX_EDX_RET(val, low, high)
-- 
2.4.3


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