Re: [PATCH] kvm/x86/vmx: switch MSR_MISC_FEATURES_ENABLES between host and guest

[Paolo Bonzini]

On 14/03/19 11:43, Xiaoyao Li wrote:
> Yes, you are right. With your patches, only when we enable cpuid faulting for
> the QEMU or other VMM userspace processes via arch_prctl, does it "leak" into
> the KVM guest. 
> 
> But arch_prctl is not the only way to enable it. We can enable cpuid faulting
> via module "msr.ko". And I think it's indeed an issue, we should not ignore it
> as it needs special cases and purpose to make it happen so far. 

Whatever is done with "msr.ko" is a non-issue.  msr.ko is at best a
debugging tool if you use it for MSRs that the kernel can write.  That
said, even the arch_prctl is an issue, as well as Peter's patch you
quote below.

The patch is a good idea even though it should be implemented in a more
efficient way.

Paolo

> Besides, Peter's this patch https://patchwork.kernel.org/patch/10850143/ is much
> likely to cause the cpuid fauting enabled in host by default during kernel
> startup. If that one is going to be applied, it's better to fix the cpuid
> faulting leak issue before that.