On Tue, Apr 20, 2021, Paolo Bonzini wrote: > From ef78673f78e3f2eedc498c1fbf9271146caa83cb Mon Sep 17 00:00:00 2001 > From: Ashish Kalra <ashish.kalra@xxxxxxx> > Date: Thu, 15 Apr 2021 15:57:02 +0000 > Subject: [PATCH 2/3] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall > > This hypercall is used by the SEV guest to notify a change in the page > encryption status to the hypervisor. The hypercall should be invoked > only when the encryption attribute is changed from encrypted -> decrypted > and vice versa. By default all guest pages are considered encrypted. > > The hypercall exits to userspace to manage the guest shared regions and > integrate with the userspace VMM's migration code. ... > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index fd4a84911355..2bc353d1f356 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -6766,3 +6766,14 @@ they will get passed on to user space. So user space still has to have > an implementation for these despite the in kernel acceleration. > > This capability is always enabled. > + > +8.32 KVM_CAP_EXIT_HYPERCALL > +--------------------------- > + > +:Capability: KVM_CAP_EXIT_HYPERCALL > +:Architectures: x86 > +:Type: vm > + > +This capability, if enabled, will cause KVM to exit to userspace > +with KVM_EXIT_HYPERCALL exit reason to process some hypercalls. > +Right now, the only such hypercall is KVM_HC_PAGE_ENC_STATUS. > diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst > index cf62162d4be2..c9378d163b5a 100644 > --- a/Documentation/virt/kvm/cpuid.rst > +++ b/Documentation/virt/kvm/cpuid.rst > @@ -96,6 +96,11 @@ KVM_FEATURE_MSI_EXT_DEST_ID 15 guest checks this feature bit > before using extended destination > ID bits in MSI address bits 11-5. > > +KVM_FEATURE_HC_PAGE_ENC_STATUS 16 guest checks this feature bit before > + using the page encryption state > + hypercall to notify the page state > + change ... > int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) > { > unsigned long nr, a0, a1, a2, a3, ret; > @@ -8334,6 +8346,28 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) > kvm_sched_yield(vcpu, a0); > ret = 0; > break; > + case KVM_HC_PAGE_ENC_STATUS: { > + u64 gpa = a0, npages = a1, enc = a2; > + > + ret = -KVM_ENOSYS; > + if (!vcpu->kvm->arch.hypercall_exit_enabled) I don't follow, why does the hypercall need to be gated by a capability? What would break if this were changed to? if (!guest_pv_has(vcpu, KVM_FEATURE_HC_PAGE_ENC_STATUS)) > + break; > + > + if (!PAGE_ALIGNED(gpa) || !npages || > + gpa_to_gfn(gpa) + npages <= gpa_to_gfn(gpa)) { > + ret = -EINVAL; > + break; > + } > + > + vcpu->run->exit_reason = KVM_EXIT_HYPERCALL; > + vcpu->run->hypercall.nr = KVM_HC_PAGE_ENC_STATUS; > + vcpu->run->hypercall.args[0] = gpa; > + vcpu->run->hypercall.args[1] = npages; > + vcpu->run->hypercall.args[2] = enc; > + vcpu->run->hypercall.longmode = op_64_bit; > + vcpu->arch.complete_userspace_io = complete_hypercall_exit; > + return 0; > + } > default: > ret = -KVM_ENOSYS; > break; ... > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 590cc811c99a..d696a9f13e33 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3258,6 +3258,14 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > vcpu->arch.msr_kvm_poll_control = data; > break; > > + case MSR_KVM_MIGRATION_CONTROL: > + if (data & ~KVM_PAGE_ENC_STATUS_UPTODATE) > + return 1; > + > + if (data && !guest_pv_has(vcpu, KVM_FEATURE_HC_PAGE_ENC_STATUS)) Why let the guest write '0'? Letting the guest do WRMSR but not RDMSR is bizarre. > + return 1; > + break; > + > case MSR_IA32_MCG_CTL: > case MSR_IA32_MCG_STATUS: > case MSR_IA32_MC0_CTL ... MSR_IA32_MCx_CTL(KVM_MAX_MCE_BANKS) - 1: > @@ -3549,6 +3557,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF)) > return 1; > > + msr_info->data = 0; > + break; > + case MSR_KVM_MIGRATION_CONTROL: > + if (!guest_pv_has(vcpu, KVM_FEATURE_HC_PAGE_ENC_STATUS)) > + return 1; > + > msr_info->data = 0; > break; > case MSR_KVM_STEAL_TIME: > -- > 2.26.2 >