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

[Brijesh Singh]

On 9/28/21 5:17 AM, Dr. David Alan Gilbert wrote:
> * 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?

Ah good catch, it should be 0x100. I will fix it.


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

In early RFC's I had a macros to build the error code but based on
feedback's went with this function with open coded values.

thanks