| Message ID | 20210122235049.3107620-4-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Revert dirty tracking for GPRs | expand |
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 { >
On Fri, Jan 22, 2021, Tom Lendacky wrote: > 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. Ah, nice! Yep, this can be dropped. Thanks!
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 {
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. 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(-)