Re: [PATCH v3 2/2] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall

[Paolo Bonzini]

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;