Re: [PATCH] Write to read-only msr MSR_IA32_PERF_STATUS is harmless, ignore it!

[Jes Sorensen <Jes.Sorensen@redhat.com>]

On 08/31/10 18:28, Avi Kivity wrote:
>  On 08/31/2010 03:17 PM, Jes.Sorensen@redhat.com wrote:
>> From: Jes Sorensen<Jes.Sorensen@redhat.com>
>>
>> We regularly see bug reports over this one, however it is a write to
>> a read-only register which some operating systems (including Linux)
>> tend to write to once in a while.
>>
>> Ignore the writes since they do no harm.
>>
> 
> Does Linux write it with wrmsr_safe()?  If not, I don't see how it
> works.  If it does, then we shouldn't ignore the write, instead issue
> the #GP as usual, but be silent about it.

To be honest, I am having a hard time determining where the write
happens. I looked at this with Gleb and the rip obtained by
kvm_read_rip(vcpu) in the code doesn't indicate anything that resembles
a wrmsr().

It was either a
560					outb(0xfe, 0x64); /* pulse reset low */
or
49		asm volatile("sti; hlt": : :"memory");

which makes no sense to me, but given it's x86, I am not sure if it
could have come from the BIOS or something during reboot?

Jes