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Date:   Tue, 28 Jun 2022 14:28:12 +0100
From:   "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To:     Ashish Kalra <Ashish.Kalra@amd.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
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Subject: Re: [PATCH Part2 v6 36/49] KVM: SVM: Add support to handle GHCB GPA
 register VMGEXIT
Message-ID: <YrsB7G4NSgJ+vKVw@work-vm>
References: <cover.1655761627.git.ashish.kalra@amd.com>
 <c2c4d365b4616c83ab2fb91b7c89d13535de8c0a.1655761627.git.ashish.kalra@amd.com>
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* 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