Re: [PATCH] KVM: Handle MSR_IA32_PERF_CTL
From: Gabriel L. Somlo
Date: Thu May 26 2016 - 16:44:46 EST
On Thu, May 26, 2016 at 10:39:31PM +0200, Radim KrÄmÃÅ wrote:
> 2016-05-26 10:32+0300, kmeaw@xxxxxxxxxxxxxx:
> > From: Dmitry Bilunov <kmeaw@xxxxxxxxxxxxxx>
> > Intel CPUs having Turbo Boost feature implement an MSR to provide a
> > control interface via rdmsr/wrmsr instructions. One could detect the
> > presence of this feature by issuing one of these instructions and
> > handling the #GP exception which is generated in case the referenced MSR
> > is not implemented by the CPU.
> > KVM's vCPU model behaves exactly as a real CPU in this case by injecting
> > a fault when MSR_IA32_PERF_CTL is called (which KVM does not support).
> > However, some operating systems use this register during an early boot
> > stage in which their kernel is not capable of handling #GP correctly,
> > causing #DP and finally a triple fault effectively resetting the vCPU.
> > This patch implements a dummy handler for MSR_IA32_PERF_CTL to avoid the
> > crashes. Most notably it fixes an issue with MacOS X 10.10 kernel.
> > Signed-off-by: Dmitry Bilunov <kmeaw@xxxxxxxxxxxxxx>
> > ---
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > @@ -2050,6 +2051,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > case MSR_VM_HSAVE_PA:
> > case MSR_AMD64_PATCH_LOADER:
> > case MSR_AMD64_BU_CFG2:
> > + case MSR_IA32_PERF_CTL:
> > break;
> Does MacOS X write it too?
After setting /sys/module/kvm/parameters/ignore_msrs, all I get in
dmesg after firing up OS X is:
vcpu0 ignored rdmsr: 0x199
So no, I don't think it would try to write it.