Re: [libvirt] [PATCH v2 3/3] KVM: VMX: enable guest access to LMCE related MSRs

On Thu, Jun 16, 2016 at 12:04:50PM +0200, Paolo Bonzini wrote: > On 16/06/2016 08:05, Haozhong Zhang wrote: > > From: Ashok Raj <ashok.raj(a)intel.com&gt; > > > > On Intel platforms, this patch adds LMCE to KVM MCE supported > > capabilities and handles guest access to LMCE related MSRs. > > > > Signed-off-by: Ashok Raj <ashok.raj(a)intel.com&gt; > > [Haozhong: macro KVM_MCE_CAP_SUPPORTED => variable kvm_mce_cap_supported > > Only enable LMCE on Intel platform > > Check MSR_IA32_FEATURE_CONTROL when handling guest > > access to MSR_IA32_MCG_EXT_CTL] > > Signed-off-by: Haozhong Zhang <haozhong.zhang(a)intel.com&gt; [...] > > @@ -6433,6 +6455,8 @@ static __init int hardware_setup(void) > > > > kvm_set_posted_intr_wakeup_handler(wakeup_handler); > > > > + kvm_mce_cap_supported |= MCG_LMCE_P; > > Ah, so virtual LMCE is available on all processors! This is > interesting, but it also makes it more complicated to handle in QEMU; a > new QEMU generally doesn't require a new kernel. > > Eduardo, any ideas? (CCing libvirt list) As we shouldn't make machine-type changes introduce new host requirements, it looks like we need to either add a new set of CPU models (unreasonable), or expect management software to explicitly enable LMCE after ensuring the host supports it. Or we could wait for a reasonable time after the feature is available in the kernel, and declare that QEMU as a whole requires a newer kernel. But how much time would be reasonable for that? Long term, I believe we should think of a better solution. I don't think it is reasonable to require new libvirt code to be written for every single low-level feature that requires a newer kernel or newer host hardware. Maybe new introspection interfaces that would allow us to drop the "no new requirements on machine-type changes" rule?