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.si...@amd.com> Cc: Tom Lendacky <thomas.lenda...@amd.com> Signed-off-by: Sean Christopherson <sea...@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 {
