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Date:   Fri, 1 Dec 2023 08:32:20 -0800
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Subject: Re: [RFC 05/33] KVM: x86: hyper-v: Introduce VTL call/return
 prologues in hypercall page
From:   Sean Christopherson <seanjc@google.com>
To:     Nicolas Saenz Julienne <nsaenz@amazon.com>
Cc:     Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
        pbonzini@redhat.com, vkuznets@redhat.com, anelkz@amazon.com,
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        kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com,
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On Fri, Dec 01, 2023, Nicolas Saenz Julienne wrote:
> > To support this I think that we can add a userspace msr filter on the HV_X64_MSR_HYPERCALL,
> > although I am not 100% sure if a userspace msr filter overrides the in-kernel msr handling.
> 
> I thought about it at the time. It's not that simple though, we should
> still let KVM set the hypercall bytecode, and other quirks like the Xen
> one.

Yeah, that Xen quirk is quite the killer.

Can you provide pseudo-assembly for what the final page is supposed to look like?
I'm struggling mightily to understand what this is actually trying to do.