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 <[email protected]>
Cc: Tom Lendacky <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
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 {
--
2.30.0.280.ga3ce27912f-goog
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 <[email protected]>
> Cc: Tom Lendacky <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> 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!