Re: [PATCH Part2 v6 36/49] KVM: SVM: Add support to handle GHCB GPA register VMGEXIT

Dr. David Alan Gilbert
2022-06-28T13:30:13Z

* Ashish Kalra (Ashish.Kalra@amd.com) wrote:
> From: Brijesh Singh <brijesh.singh@amd.com>
>
> SEV-SNP guests are required to perform a GHCB GPA registration. Before
> using a GHCB GPA for a vCPU the first time, a guest must register the
> vCPU GHCB GPA. If hypervisor can work with the guest requested GPA then
> it must respond back with the same GPA otherwise return -1.
>
> On VMEXIT, Verify that GHCB GPA matches with the registered value. If a
> mismatch is detected then abort the guest.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/include/asm/sev-common.h | 8 ++++++++
> arch/x86/kvm/svm/sev.c | 27 +++++++++++++++++++++++++++
> arch/x86/kvm/svm/svm.h | 7 +++++++
> 3 files changed, 42 insertions(+)
>
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 539de6b93420..0a9055cdfae2 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -59,6 +59,14 @@
> #define GHCB_MSR_AP_RESET_HOLD_RESULT_POS 12
> #define GHCB_MSR_AP_RESET_HOLD_RESULT_MASK GENMASK_ULL(51, 0)
>
> +/* Preferred GHCB GPA Request */
> +#define GHCB_MSR_PREF_GPA_REQ 0x010
> +#define GHCB_MSR_GPA_VALUE_POS 12
> +#define GHCB_MSR_GPA_VALUE_MASK GENMASK_ULL(51, 0)

Are the magic 51's in here fixed ?

Dave

> +#define GHCB_MSR_PREF_GPA_RESP 0x011
> +#define GHCB_MSR_PREF_GPA_NONE 0xfffffffffffff
> +
> /* GHCB GPA Register */
> #define GHCB_MSR_REG_GPA_REQ 0x012
> #define GHCB_MSR_REG_GPA_REQ_VAL(v) \
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c70f3f7e06a8..6de48130e414 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3331,6 +3331,27 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
> GHCB_MSR_INFO_MASK, GHCB_MSR_INFO_POS);
> break;
> }
> + case GHCB_MSR_PREF_GPA_REQ: {
> + set_ghcb_msr_bits(svm, GHCB_MSR_PREF_GPA_NONE, GHCB_MSR_GPA_VALUE_MASK,
> + GHCB_MSR_GPA_VALUE_POS);
> + set_ghcb_msr_bits(svm, GHCB_MSR_PREF_GPA_RESP, GHCB_MSR_INFO_MASK,
> + GHCB_MSR_INFO_POS);
> + break;
> + }
> + case GHCB_MSR_REG_GPA_REQ: {
> + u64 gfn;
> +
> + gfn = get_ghcb_msr_bits(svm, GHCB_MSR_GPA_VALUE_MASK,
> + GHCB_MSR_GPA_VALUE_POS);
> +
> + svm->sev_es.ghcb_registered_gpa = gfn_to_gpa(gfn);
> +
> + set_ghcb_msr_bits(svm, gfn, GHCB_MSR_GPA_VALUE_MASK,
> + GHCB_MSR_GPA_VALUE_POS);
> + set_ghcb_msr_bits(svm, GHCB_MSR_REG_GPA_RESP, GHCB_MSR_INFO_MASK,
> + GHCB_MSR_INFO_POS);
> + break;
> + }
> case GHCB_MSR_TERM_REQ: {
> u64 reason_set, reason_code;
>
> @@ -3381,6 +3402,12 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> + /* SEV-SNP guest requires that the GHCB GPA must be registered */
> + if (sev_snp_guest(svm->vcpu.kvm) && !ghcb_gpa_is_registered(svm, ghcb_gpa)) {
> + vcpu_unimpl(&svm->vcpu, "vmgexit: GHCB GPA [%#llx] is not registered.\n", ghcb_gpa);
> + return -EINVAL;
> + }
> +
> ret = sev_es_validate_vmgexit(svm, &exit_code);
> if (ret)
> return ret;
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index c80352c9c0d6..54ff56cb6125 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -206,6 +206,8 @@ struct vcpu_sev_es_state {
> */
> u64 ghcb_sw_exit_info_1;
> u64 ghcb_sw_exit_info_2;
> +
> + u64 ghcb_registered_gpa;
> };
>
> struct vcpu_svm {
> @@ -334,6 +336,11 @@ static inline bool sev_snp_guest(struct kvm *kvm)
> return sev_es_guest(kvm) && sev->snp_active;
> }
>
> +static inline bool ghcb_gpa_is_registered(struct vcpu_svm *svm, u64 val)
> +{
> + return svm->sev_es.ghcb_registered_gpa == val;
> +}
> +
> static inline void vmcb_mark_all_dirty(struct vmcb *vmcb)
> {
> vmcb->control.clean = 0;
> --
> 2.25.1
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK