Re: problem wit svm_get_msr on kvm-kmod-2.6.31.6

[Jan Kiszka <jan.kiszka@siemens.com>]

Avi Kivity wrote:
> On 11/16/2009 01:17 PM, Dietmar Maurer wrote:
>>      38f0:       0f 85 82 01 00 00       jne    3a78<svm_get_msr+0x2b8>
>>      38f6:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>>      38fd:       48 8b 48 50             mov    0x50(%rax),%rcx
>>      3901:       0f 31                   rdtsc
>>      3903:       48 01 c8                add    %rcx,%rax
>>
>> # this is svm_get_msr+0x146
>>      3906:       48 89 02                mov    %rax,(%rdx)
>>    
> 
> 
> Looks like a miscompile of native_read_tsc(), it needs to use %edx:%eax, 
> not assume the result is in %rax.
> 
> Jan, looks like the culprit is
> 
>    static inline unsigned long long kvm_native_read_tsc(void)
>    {
>          unsigned long long val;
>          asm volatile("rdtsc" : "=A" (val));
>          return val;
>    }
> 
> "=A" only works correctly on i386, need to use "=a" "=d" for portability.
> 

Yes, already commit a fix, currently propagating it through all series.

Jan

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