Messages in this thread | | | Subject | Re: [PATCH 3/3] KVM: SVM: Sync GPRs to the GHCB only after VMGEXIT | From | Tom Lendacky <> | Date | Fri, 22 Jan 2021 18:09:31 -0600 |
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On 1/22/21 5:50 PM, Sean Christopherson wrote: > Sync GPRs to the GHCB on VMRUN only if a sync is needed, i.e. if the > previous exit was a VMGEXIT and the guest is expecting some data back. >
The start of sev_es_sync_to_ghcb() checks if the GHCB has been mapped, which only occurs on VMGEXIT, and exits early if not. And sev_es_sync_from_ghcb() is only called if the GHCB has been successfully mapped. The only thing in between is sev_es_validate_vmgexit(), which will terminate the VM on error. So I don't think this patch is needed.
Thanks, Tom
> Cc: Brijesh Singh <brijesh.singh@amd.com> > Cc: Tom Lendacky <thomas.lendacky@amd.com> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > arch/x86/kvm/svm/sev.c | 15 ++++++++++----- > arch/x86/kvm/svm/svm.h | 1 + > 2 files changed, 11 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index ac652bc476ae..9bd1e1650eb3 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -1418,10 +1418,13 @@ static void sev_es_sync_to_ghcb(struct vcpu_svm *svm) > * Copy their values, even if they may not have been written during the > * VM-Exit. It's the guest's responsibility to not consume random data. > */ > - ghcb_set_rax(ghcb, vcpu->arch.regs[VCPU_REGS_RAX]); > - ghcb_set_rbx(ghcb, vcpu->arch.regs[VCPU_REGS_RBX]); > - ghcb_set_rcx(ghcb, vcpu->arch.regs[VCPU_REGS_RCX]); > - ghcb_set_rdx(ghcb, vcpu->arch.regs[VCPU_REGS_RDX]); > + if (svm->need_sync_to_ghcb) { > + ghcb_set_rax(ghcb, vcpu->arch.regs[VCPU_REGS_RAX]); > + ghcb_set_rbx(ghcb, vcpu->arch.regs[VCPU_REGS_RBX]); > + ghcb_set_rcx(ghcb, vcpu->arch.regs[VCPU_REGS_RCX]); > + ghcb_set_rdx(ghcb, vcpu->arch.regs[VCPU_REGS_RDX]); > + svm->need_sync_to_ghcb = false; > + } > } > > static void sev_es_sync_from_ghcb(struct vcpu_svm *svm) > @@ -1441,8 +1444,10 @@ static void sev_es_sync_from_ghcb(struct vcpu_svm *svm) > * VMMCALL allows the guest to provide extra registers. KVM also > * expects RSI for hypercalls, so include that, too. > * > - * Copy their values to the appropriate location if supplied. > + * Copy their values to the appropriate location if supplied, and > + * flag that a sync back to the GHCB is needed on the next VMRUN. > */ > + svm->need_sync_to_ghcb = true; > memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs)); > > vcpu->arch.regs[VCPU_REGS_RAX] = ghcb_get_rax_if_valid(ghcb); > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h > index 0fe874ae5498..4e2e5f9fbfc2 100644 > --- a/arch/x86/kvm/svm/svm.h > +++ b/arch/x86/kvm/svm/svm.h > @@ -192,6 +192,7 @@ struct vcpu_svm { > u64 ghcb_sa_len; > bool ghcb_sa_sync; > bool ghcb_sa_free; > + bool need_sync_to_ghcb; > }; > > struct svm_cpu_data { >
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