Re: [PATCH] KVM: x86: Update Xen-specific CPUID leaves during mangling

David Woodhouse
2025-01-22T18:53:45Z

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On Wed, 2025-01-22 at 18:44 +0100, Vitaly Kuznetsov wrote:
>
> >
> > What is the purpose of the comparison anyway? IIUC we want to ensure
> > that a VMM does not change its mind after KVM_RUN so should we not be
> > stashing what was set by the VMM and comparing against that *before*
> > mangling any values?
> >
>
> I guess it can be done this way but we will need to keep these 'original'
> unmangled values for the lifetime of the vCPU with very little gain (IMO):
> KVM_SET_CPUID{,2} either fails (if the data is different) or does (almost)
> nothing when the data is the same.

If they're supposed to be entirely unchanged, would it suffice just to
keep a hash of them?

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