Re: [PATCH Part2 v5 38/45] KVM: SVM: Add support to handle Page State Change VMGEXIT

[Dr. David Alan Gilbert]

* Brijesh Singh (brijesh.singh@xxxxxxx) wrote:
> SEV-SNP VMs can ask the hypervisor to change the page state in the RMP
> table to be private or shared using the Page State Change NAE event
> as defined in the GHCB specification version 2.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> ---
>  arch/x86/include/asm/sev-common.h |  7 +++
>  arch/x86/kvm/svm/sev.c            | 82 +++++++++++++++++++++++++++++--
>  2 files changed, 84 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 4980f77aa1d5..5ee30bb2cdb8 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -126,6 +126,13 @@ enum psc_op {
>  /* SNP Page State Change NAE event */
>  #define VMGEXIT_PSC_MAX_ENTRY		253
>  
> +/* The page state change hdr structure in not valid */
> +#define PSC_INVALID_HDR			1
> +/* The hdr.cur_entry or hdr.end_entry is not valid */
> +#define PSC_INVALID_ENTRY		2
> +/* Page state change encountered undefined error */
> +#define PSC_UNDEF_ERR			3
> +
>  struct psc_hdr {
>  	u16 cur_entry;
>  	u16 end_entry;
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 6d9483ec91ab..0de85ed63e9b 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2731,6 +2731,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm, u64 *exit_code)
>  	case SVM_VMGEXIT_AP_JUMP_TABLE:
>  	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>  	case SVM_VMGEXIT_HV_FEATURES:
> +	case SVM_VMGEXIT_PSC:
>  		break;
>  	default:
>  		goto vmgexit_err;
> @@ -3004,13 +3005,13 @@ static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op,
>  		 */
>  		rc = snp_check_and_build_npt(vcpu, gpa, level);
>  		if (rc)
> -			return -EINVAL;
> +			return PSC_UNDEF_ERR;
>  
>  		if (op == SNP_PAGE_STATE_PRIVATE) {
>  			hva_t hva;
>  
>  			if (snp_gpa_to_hva(kvm, gpa, &hva))
> -				return -EINVAL;
> +				return PSC_UNDEF_ERR;
>  
>  			/*
>  			 * Verify that the hva range is registered. This enforcement is
> @@ -3022,7 +3023,7 @@ static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op,
>  			rc = is_hva_registered(kvm, hva, page_level_size(level));
>  			mutex_unlock(&kvm->lock);
>  			if (!rc)
> -				return -EINVAL;
> +				return PSC_UNDEF_ERR;
>  
>  			/*
>  			 * Mark the userspace range unmerable before adding the pages
> @@ -3032,7 +3033,7 @@ static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op,
>  			rc = snp_mark_unmergable(kvm, hva, page_level_size(level));
>  			mmap_write_unlock(kvm->mm);
>  			if (rc)
> -				return -EINVAL;
> +				return PSC_UNDEF_ERR;
>  		}
>  
>  		write_lock(&kvm->mmu_lock);
> @@ -3062,8 +3063,11 @@ static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op,
>  		case SNP_PAGE_STATE_PRIVATE:
>  			rc = rmp_make_private(pfn, gpa, level, sev->asid, false);
>  			break;
> +		case SNP_PAGE_STATE_PSMASH:
> +		case SNP_PAGE_STATE_UNSMASH:
> +			/* TODO: Add support to handle it */
>  		default:
> -			rc = -EINVAL;
> +			rc = PSC_INVALID_ENTRY;
>  			break;
>  		}
>  
> @@ -3081,6 +3085,65 @@ static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op,
>  	return 0;
>  }
>  
> +static inline unsigned long map_to_psc_vmgexit_code(int rc)
> +{
> +	switch (rc) {
> +	case PSC_INVALID_HDR:
> +		return ((1ul << 32) | 1);
> +	case PSC_INVALID_ENTRY:
> +		return ((1ul << 32) | 2);
> +	case RMPUPDATE_FAIL_OVERLAP:
> +		return ((3ul << 32) | 2);
> +	default: return (4ul << 32);
> +	}

Are these the values defined in 56421 section 4.1.6 ?
If so, that says:
  SW_EXITINFO2[63:32] == 0x00000100
      The hypervisor encountered some other error situation and was not able to complete the
      request identified by page_state_change_header.cur_entry. It is left to the guest to decide how
      to proceed in this situation.

so it looks like the default should be 0x100 rather than 4?

(It's a shame they're all magical constants, it would be nice if the
standard have them names)

Dave


> +}
> +
> +static unsigned long snp_handle_page_state_change(struct vcpu_svm *svm)
> +{
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	int level, op, rc = PSC_UNDEF_ERR;
> +	struct snp_psc_desc *info;
> +	struct psc_entry *entry;
> +	u16 cur, end;
> +	gpa_t gpa;
> +
> +	if (!sev_snp_guest(vcpu->kvm))
> +		return PSC_INVALID_HDR;
> +
> +	if (!setup_vmgexit_scratch(svm, true, sizeof(*info))) {
> +		pr_err("vmgexit: scratch area is not setup.\n");
> +		return PSC_INVALID_HDR;
> +	}
> +
> +	info = (struct snp_psc_desc *)svm->ghcb_sa;
> +	cur = info->hdr.cur_entry;
> +	end = info->hdr.end_entry;
> +
> +	if (cur >= VMGEXIT_PSC_MAX_ENTRY ||
> +	    end >= VMGEXIT_PSC_MAX_ENTRY || cur > end)
> +		return PSC_INVALID_ENTRY;
> +
> +	for (; cur <= end; cur++) {
> +		entry = &info->entries[cur];
> +		gpa = gfn_to_gpa(entry->gfn);
> +		level = RMP_TO_X86_PG_LEVEL(entry->pagesize);
> +		op = entry->operation;
> +
> +		if (!IS_ALIGNED(gpa, page_level_size(level))) {
> +			rc = PSC_INVALID_ENTRY;
> +			goto out;
> +		}
> +
> +		rc = __snp_handle_page_state_change(vcpu, op, gpa, level);
> +		if (rc)
> +			goto out;
> +	}
> +
> +out:
> +	info->hdr.cur_entry = cur;
> +	return rc ? map_to_psc_vmgexit_code(rc) : 0;
> +}
> +
>  static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
>  {
>  	struct vmcb_control_area *control = &svm->vmcb->control;
> @@ -3315,6 +3378,15 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
>  		ret = 1;
>  		break;
>  	}
> +	case SVM_VMGEXIT_PSC: {
> +		unsigned long rc;
> +
> +		ret = 1;
> +
> +		rc = snp_handle_page_state_change(svm);
> +		svm_set_ghcb_sw_exit_info_2(vcpu, rc);
> +		break;
> +	}
>  	case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>  		vcpu_unimpl(vcpu,
>  			    "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
> -- 
> 2.17.1
> 
> 
-- 
Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK