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

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Aug 31, 2010 at 06:33:34PM +0200, 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, but given it's x86, I am not sure if it
> could have come from the BIOS or something during reboot?
> 
> Jes

kvm_reset_msrs in qemu-kvm-x86.c.