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>
>
> 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>
> [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>
[...]
> @@ -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?
--
Eduardo