On 08/31/10 18:44, Avi Kivity wrote: > 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@xxxxxxxxxx wrote: >>>> From: Jes Sorensen<Jes.Sorensen@xxxxxxxxxx> >>>> >>>> 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. Been there, done that! This happens with an F13 kernel during reboot. Ran the search on the expanded 2.6.32.8-149 tree and found no reference to anything trying to write it, except for KVM backing up the flag, but that shouldn't happen in the guest. >> 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). I was fooled by this too, it's not a performance counter MSR, it's a CPU frequency scaling MSR. Cheers, Jes -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html