Re: Revert "x86/speculation: Simplify indirect_branch_prediction_barrier()" crashes KVM guest

[Richard Weinberger]

Am Freitag, 16. Februar 2018, 00:28:30 CET schrieb David Woodhouse:
> On Fri, 2018-02-16 at 00:12 +0100, Richard Weinberger wrote:
> > [    2.791518] Code: 8b 45 00 49 8b 7d 08 49 83 c5 18 31 d2 31 f6 ff
> > d0 49 8b 45 00 48 85 c0 75 e9 eb b1 b9 49 00 00 00 b8 01 00 00 00 ba
> > 00 00 00 00 <0f> 30 e9 68 fd ff ff 9c 58 0f 1f 44 00 00 48 89 c5 fa
> > 66 0f 1f
> 
>   23:   b9 49 00 00 00          mov    $0x49,%ecx
>   28:   b8 01 00 00 00          mov    $0x1,%eax
>   2d:   ba 00 00 00 00          mov    $0x0,%edx
>   32:   0f 30                   wrmsr  
> 
> The faulting instruction is the wrmsr itself. That shouldn't happen; if
> the CPUID bit indicates that the MSR exists, then it should exist.
> 
> The reverted patch did use the C __wrmsr() macro which contained a
> fixup for this GP# but it was just a side-effect of the "cleanup" â it
> wasn't intentional because that really shouldn't happen. That looks
> like a qemu bug as first glance.

Hmmm, yes seems so. Just gave latest qemu a try, works fine. ;-\

Thanks,
//richard

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