Re: [PATCH 3/4] KVM: nVMX: accurate emulation of MSR_IA32_CR{0,4}_FIXED1

[Paolo Bonzini]

On 23/11/2016 23:07, David Matlack wrote:
> A downside of this scheme is we'd have to remember to update
> nested_vmx_cr4_fixed1_update() before giving VMs new CPUID bits. If we
> forget, a VM could end up with different values for CR{0,4}_FIXED0 for
> the same CPUID depending on which version of KVM you're running on.

If userspace doesn't obey KVM_GET_SUPPORTED_CPUID, all bets are off
anyway, so I don't think it's a big deal.  However, if you want to make
it generated by userspace, that would be fine as well!  That would
simply entail removing this patch, wouldn't it?

Paolo

> Hm, now I'm thinking you were right in the beginning. Userspace should
> generate CR{0,4}_FIXED1, not the kernel. And KVM should allow
> userspace to save/restore them.