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SubjectRe: [PATCH v3 2/2] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall
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On 04/05/21 19:09, Sean Christopherson wrote:
> On Sat, May 01, 2021, Paolo Bonzini wrote:
>> - make it completely independent from migration, i.e. it's just a facet of
>> MSR_KVM_PAGE_ENC_STATUS saying whether the bitmap is up-to-date. It would
>> use CPUID bit as the encryption status bitmap and have no code at all in KVM
>> (userspace needs to set up the filter and implement everything).
>
> If the bit is purely a "page encryption status is up-to-date", what about
> overloading KVM_HC_PAGE_ENC_STATUS to handle that status update as well? That
> would eliminate my biggest complaint about having what is effectively a single
> paravirt feature split into two separate, but intertwined chunks of ABI.

It's true that they are intertwined, but I dislike not having a way to
read the current state.

Paolo

>
> #define KVM_HC_PAGE_ENC_UPDATE 12
>
> #define KVM_HC_PAGE_ENC_REGION_UPDATE 0 /* encrypted vs. plain text */
> #define KVM_HC_PAGE_ENC_STATUS_UPDATE 1 /* up-to-date vs. stale */
>
> ret = -KVM_ENOSYS;
> if (!vcpu->kvm->arch.hypercall_exit_enabled)
> break;
>
> ret = -EINVAL;
> if (a0 == KVM_HC_PAGE_ENC_REGION_UPDATE) {
> u64 gpa = a1, npages = a2;
>
> if (!PAGE_ALIGNED(gpa) || !npages ||
> gpa_to_gfn(gpa) + npages <= gpa_to_gfn(gpa))
> break;
> } else if (a0 != KVM_HC_PAGE_ENC_STATUS_UPDATE) {
> break;
> }
>
> vcpu->run->exit_reason = KVM_EXIT_HYPERCALL;
> vcpu->run->hypercall.nr = KVM_HC_PAGE_ENC_STATUS;
> vcpu->run->hypercall.args[0] = a0;
> vcpu->run->hypercall.args[1] = a1;
> vcpu->run->hypercall.args[2] = a2;
> vcpu->run->hypercall.args[3] = a3;
> vcpu->run->hypercall.longmode = op_64_bit;
> vcpu->arch.complete_userspace_io = complete_hypercall_exit;
> return 0;
>

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