Date: Wed, 14 Feb 2024 18:03:47 -0600
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<seanjc@...gle.com>, <aik@....com>, <isaku.yamahata@...el.com>
Subject: Re: [PATCH 05/10] KVM: SEV: store VMSA features in kvm_sev_info

On Fri, Feb 09, 2024 at 01:37:37PM -0500, Paolo Bonzini wrote:
> Right now, the set of features that are stored in the VMSA upon
> initialization is fixed and depends on the module parameters for
> kvm-amd.ko.  However, the hypervisor cannot really change it at will
> because the feature word has to match between the hypervisor and whatever
> computes a measurement of the VMSA for attestation purposes.
> 
> Add a field to kvm_set_info that holds the set of features to be stored

s/kvm_set_info_/kvm_sev_info/

Otherwise:

Reviewed-by: Michael Roth <michael.roth@....com>

> in the VMSA; and query it instead of referring to the module parameters.
> 
> Because KVM_SEV_INIT and KVM_SEV_ES_INIT accept no parameters, this
> does not yet introduce any functional change, but it paves the way for
> an API that allows customization of the features per-VM.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/svm/sev.c | 22 ++++++++++++++++++----
>  arch/x86/kvm/svm/svm.c |  2 +-
>  arch/x86/kvm/svm/svm.h |  3 ++-
>  3 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 2e558f7538c2..712bfbc0028a 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -116,6 +116,14 @@ static inline bool is_mirroring_enc_context(struct kvm *kvm)
>  	return !!to_kvm_svm(kvm)->sev_info.enc_context_owner;
>  }
> 
> +static bool sev_vcpu_has_debug_swap(struct vcpu_svm *svm)
> +{
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info;
> +
> +	return sev->vmsa_features & SVM_SEV_FEAT_DEBUG_SWAP;
> +}
> +
>  /* Must be called with the sev_bitmap_lock held */
>  static bool __sev_recycle_asids(int min_asid, int max_asid)
>  {
> @@ -258,6 +266,8 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
> 
>  	sev->active = true;
>  	sev->es_active = argp->id == KVM_SEV_ES_INIT;
> +	sev->vmsa_features = sev_supported_vmsa_features;
> +
>  	asid = sev_asid_new(sev);
>  	if (asid < 0)
>  		goto e_no_asid;
> @@ -278,6 +288,7 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	sev_asid_free(sev);
>  	sev->asid = 0;
>  e_no_asid:
> +	sev->vmsa_features = 0;
>  	sev->es_active = false;
>  	sev->active = false;
>  	return ret;
> @@ -572,6 +583,8 @@ static int sev_launch_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
> 
>  static int sev_es_sync_vmsa(struct vcpu_svm *svm)
>  {
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info;
>  	struct sev_es_save_area *save = svm->sev_es.vmsa;
> 
>  	/* Check some debug related fields before encrypting the VMSA */
> @@ -613,7 +626,7 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
>  	save->xss  = svm->vcpu.arch.ia32_xss;
>  	save->dr6  = svm->vcpu.arch.dr6;
> 
> -	save->sev_features = sev_supported_vmsa_features;
> +	save->sev_features = sev->vmsa_features;
> 
>  	pr_debug("Virtual Machine Save Area (VMSA):\n");
>  	print_hex_dump_debug("", DUMP_PREFIX_NONE, 16, 1, save, sizeof(*save), false);
> @@ -1693,6 +1706,7 @@ static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
>  	dst->pages_locked = src->pages_locked;
>  	dst->enc_context_owner = src->enc_context_owner;
>  	dst->es_active = src->es_active;
> +	dst->vmsa_features = src->vmsa_features;
> 
>  	src->asid = 0;
>  	src->active = false;
> @@ -3063,7 +3077,7 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
>  	svm_set_intercept(svm, TRAP_CR8_WRITE);
> 
>  	vmcb->control.intercepts[INTERCEPT_DR] = 0;
> -	if (!sev_es_debug_swap_enabled) {
> +	if (!sev_vcpu_has_debug_swap(svm)) {
>  		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
>  		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
>  		recalc_intercepts(svm);
> @@ -3118,7 +3132,7 @@ void sev_es_vcpu_reset(struct vcpu_svm *svm)
>  					    sev_enc_bit));
>  }
> 
> -void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa)
> +void sev_es_prepare_switch_to_guest(struct vcpu_svm *svm, struct sev_es_save_area *hostsa)
>  {
>  	/*
>  	 * All host state for SEV-ES guests is categorized into three swap types
> @@ -3146,7 +3160,7 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa)
>  	 * the CPU (Type-B). If DebugSwap is disabled/unsupported, the CPU both
>  	 * saves and loads debug registers (Type-A).
>  	 */
> -	if (sev_es_debug_swap_enabled) {
> +	if (sev_vcpu_has_debug_swap(svm)) {
>  		hostsa->dr0 = native_get_debugreg(0);
>  		hostsa->dr1 = native_get_debugreg(1);
>  		hostsa->dr2 = native_get_debugreg(2);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index aa1792f402ab..392b9c2e2ce1 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1523,7 +1523,7 @@ static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>  		struct sev_es_save_area *hostsa;
>  		hostsa = (struct sev_es_save_area *)(page_address(sd->save_area) + 0x400);
> 
> -		sev_es_prepare_switch_to_guest(hostsa);
> +		sev_es_prepare_switch_to_guest(svm, hostsa);
>  	}
> 
>  	if (tsc_scaling)
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index d630026b23b0..864c782eaa58 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -85,6 +85,7 @@ struct kvm_sev_info {
>  	unsigned long pages_locked; /* Number of pages locked */
>  	struct list_head regions_list;  /* List of registered regions */
>  	u64 ap_jump_table;	/* SEV-ES AP Jump Table address */
> +	u64 vmsa_features;
>  	struct kvm *enc_context_owner; /* Owner of copied encryption context */
>  	struct list_head mirror_vms; /* List of VMs mirroring */
>  	struct list_head mirror_entry; /* Use as a list entry of mirrors */
> @@ -693,7 +694,7 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu);
>  int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in);
>  void sev_es_vcpu_reset(struct vcpu_svm *svm);
>  void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector);
> -void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa);
> +void sev_es_prepare_switch_to_guest(struct vcpu_svm *svm, struct sev_es_save_area *hostsa);
>  void sev_es_unmap_ghcb(struct vcpu_svm *svm);
> 
>  /* vmenter.S */
> -- 
> 2.39.0
> 
> 
> 

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