Re: [PATCH 1/5] KVM: x86/xen: Restrict hypercall MSR to unofficial synthetic range

[David Woodhouse]

On Wed, 2025-02-05 at 16:18 +0000, David Woodhouse wrote:
> 
> > Oh!  It doesn't help KVM avoid breaking userspace, but a way for QEMU to avoid a
> > future collision would be to have QEMU start at 0x40000200 when Hyper-V is enabled,
> > but then use KVM_GET_MSR_INDEX_LIST to detect a collision with KVM Hyper-V, e.g.
> > increment the index until an available index is found (with sanity checks and whatnot).
> 
> Makes sense. I think that's a third separate patch, yes?

To be clear, I think I mean a third patch which further restricts
kvm_xen_hvm_config() to disallow indices for which
kvm_is_advertised_msr() returns true?

We could roll that into your original patch instead, if you prefer.

Q: Should kvm_is_advertised_msr() include the Xen hypercall MSR, if one
is already configured? Life is easier if we answer 'no'...

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