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

[Avi Kivity <avi@redhat.com>]

  On 08/31/2010 07:33 PM, Jes Sorensen wrote:
> 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,

Just grep for the msr name in a guest kernel source that's known to 
trigger the message.

>   but given it's x86, I am not sure if it
> could have come from the BIOS or something during reboot?

The bios is the same for all kernels (and is unlikely to mess with 
performance counter msrs anyway).


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