diff mbox series

[2/2] KVM: SVM: Provide helpers to set the error code

Message ID 20241206221257.7167-3-huibo.wang@amd.com (mailing list archive)
State New
Headers show
Series KVM: SVM: Make VMGEXIT GHCB exit codes more readable | expand

Commit Message

Melody Wang Dec. 6, 2024, 10:12 p.m. UTC 
Provide helpers to set the error code when converting VMGEXIT SW_EXITINFO1 and
SW_EXITINFO2 codes from plain numbers to proper defines. Add comments for
better code readability.

No functionality changed.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Melody Wang <huibo.wang@amd.com>
---
 arch/x86/kvm/svm/sev.c | 39 +++++++++++++++++++++------------------
 arch/x86/kvm/svm/svm.c |  6 +-----
 arch/x86/kvm/svm/svm.h | 24 ++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 23 deletions(-)

Comments

Sean Christopherson Dec. 17, 2024, 12:56 a.m. UTC | #1 
On Fri, Dec 06, 2024, Melody Wang wrote:
> @@ -3577,8 +3576,7 @@ static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
>  	return 0;
>  
>  e_scratch:
> -	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_MALFORMED_INPUT);
> -	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_SCRATCH_AREA);
> +	svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_SCRATCH_AREA);
>  
>  	return 1;
>  }
> @@ -3671,7 +3669,11 @@ static void snp_complete_psc(struct vcpu_svm *svm, u64 psc_ret)
>  	svm->sev_es.psc_inflight = 0;
>  	svm->sev_es.psc_idx = 0;
>  	svm->sev_es.psc_2m = false;
> -	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, psc_ret);
> +	/*
> +	 * psc_ret contains 0 if all entries have been processed successfully

No, it doesn't.

  • SW_EXITINFO2 == 0x00000000
    The page state change request was interrupted, retry the request.

> +	 * or a reason code identifying why the request has not completed.

Honestly, even if it were correct, this comment does far more harm than good.
The literal '0' below has nothing to do with the '0' referenced in the comment,
and so all the comment does is add more confusion.  Furthermore, this is the
wrong place to document SW_EXITINFO2 return codes.  That's the responsibility of
the call sites and/or individual PSC-specific macros.

This code should instead document the weirdness with PSC's SW_EXITINFO1:

	/*
	 * Because the GHCB says so, PSC requests always get a "no action"
	 * response, with a PSC-specific return code in SW_EXITINFO2.
	 *
	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_NO_ACTION, psc_ret);

The readers of _this_ code don't care about the individual return codes, they
care about knowing the semantics of the return itself.

Alternatively, it might even make sense to add a svm_vmgexit_no_action() helper
(along with svm_vmgexit_success()).  There are at least two VMGEXIT types that
roll their own error codes with NO_ACTION, and it might be better to have the
initial zeroing in sev_handle_vmgexit() use NO_ACTION, e.g.

	/*
	 * Assume no action is required as the vast majority of VMGEXITs don't
	 * require the guest to take action upon success, and initializing the
	 * GHCB for the happy case avoids the need to do so for exits that are
	 * handled via SVM's common exit handlers.
	 */
	svm_vmgexit_no_action(svm, 0);

> +	 */
> +	svm_vmgexit_set_return_code(svm, 0, psc_ret);
>  }
>  
>  static void __snp_complete_one_psc(struct vcpu_svm *svm)
> @@ -4067,8 +4069,12 @@ static int snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_
>  		ret = -EIO;
>  		goto out_unlock;
>  	}
> -
> -	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(0, fw_err));
> +	/*
> +	 * SNP_GUEST_ERR(0, fw_err): Upper 32-bits (63:32) will contain the
> +	 * return code from the hypervisor. Lower 32-bits (31:0) will contain
> +	 * the return code from the firmware call (0 = success)

Same thing here.  A comment documenting SNP_GUEST_ERR() belongs above the
definition of SNP_GUEST_ERR.  How the "guest error code" is constructed isn't
relevant/unique to this code, what's relevant is that *KVM* isn't requesting an
action.

	/*
	 * No action is requested from KVM, even if the request failed due to a
	 * firmware error.
	 */
	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_NO_ACTION,
				    SNP_GUEST_ERR(0, fw_err));


> +	 */
> +	svm_vmgexit_set_return_code(svm, 0, SNP_GUEST_ERR(0, fw_err));
>  
>  	ret = 1; /* resume guest */
>  

...

> +static inline void svm_vmgexit_set_return_code(struct vcpu_svm *svm,
> +						u64 response, u64 data)
> +{
> +	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, response);
> +	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, data);
> +}
> +
> +static inline void svm_vmgexit_inject_exception(struct vcpu_svm *svm, u8 vector)
> +{
> +	u64 data = SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_EXEPT | vector;
> +
> +	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_ISSUE_EXCEPTION, data);
> +}
> +
> +static inline void svm_vmgexit_bad_input(struct vcpu_svm *svm, u64 suberror)
> +{
> +	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_MALFORMED_INPUT, suberror);
> +}
> +
> +static inline void svm_vmgexit_success(struct vcpu_svm *svm, u64 data)

As mentioned in patch 1, please keep svm_vmgexit_success() even if
GHCB_HV_RESP_SUCCESS is renamed to GHCB_HV_RESP_NO_ACTION.

> +{
> +	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_SUCCESS, data);
> +}
> +
>  /* svm.c */
>  #define MSR_INVALID				0xffffffffU
>  
> -- 
> 2.34.1
>
diff mbox series

Patch

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index e7db7a5703b7..409f77a6151e 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3433,8 +3433,7 @@  static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
 		dump_ghcb(svm);
 	}
 
-	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_MALFORMED_INPUT);
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, reason);
+	svm_vmgexit_bad_input(svm, reason);
 
 	/* Resume the guest to "return" the error code. */
 	return 1;
@@ -3577,8 +3576,7 @@  static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
 	return 0;
 
 e_scratch:
-	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_MALFORMED_INPUT);
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_SCRATCH_AREA);
+	svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_SCRATCH_AREA);
 
 	return 1;
 }
@@ -3671,7 +3669,11 @@  static void snp_complete_psc(struct vcpu_svm *svm, u64 psc_ret)
 	svm->sev_es.psc_inflight = 0;
 	svm->sev_es.psc_idx = 0;
 	svm->sev_es.psc_2m = false;
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, psc_ret);
+	/*
+	 * psc_ret contains 0 if all entries have been processed successfully
+	 * or a reason code identifying why the request has not completed.
+	 */
+	svm_vmgexit_set_return_code(svm, 0, psc_ret);
 }
 
 static void __snp_complete_one_psc(struct vcpu_svm *svm)
@@ -4067,8 +4069,12 @@  static int snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_
 		ret = -EIO;
 		goto out_unlock;
 	}
-
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(0, fw_err));
+	/*
+	 * SNP_GUEST_ERR(0, fw_err): Upper 32-bits (63:32) will contain the
+	 * return code from the hypervisor. Lower 32-bits (31:0) will contain
+	 * the return code from the firmware call (0 = success)
+	 */
+	svm_vmgexit_set_return_code(svm, 0, SNP_GUEST_ERR(0, fw_err));
 
 	ret = 1; /* resume guest */
 
@@ -4124,8 +4130,7 @@  static int snp_handle_ext_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t r
 	return snp_handle_guest_req(svm, req_gpa, resp_gpa);
 
 request_invalid:
-	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_MALFORMED_INPUT);
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_INPUT);
+	svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
 	return 1; /* resume guest */
 }
 
@@ -4317,8 +4322,7 @@  int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 	if (ret)
 		return ret;
 
-	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_SUCCESS);
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, 0);
+	svm_vmgexit_success(svm, 0);
 
 	exit_code = kvm_ghcb_get_sw_exit_code(control);
 	switch (exit_code) {
@@ -4362,20 +4366,20 @@  int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 			break;
 		case 1:
 			/* Get AP jump table address */
-			ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, sev->ap_jump_table);
+			svm_vmgexit_set_return_code(svm, 0, sev->ap_jump_table);
 			break;
 		default:
 			pr_err("svm: vmgexit: unsupported AP jump table request - exit_info_1=%#llx\n",
 			       control->exit_info_1);
-			ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_MALFORMED_INPUT);
-			ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_INPUT);
+			svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
 		}
 
 		ret = 1;
 		break;
 	}
 	case SVM_VMGEXIT_HV_FEATURES:
-		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_HV_FT_SUPPORTED);
+		/* Get hypervisor supported features */
+		svm_vmgexit_success(svm, GHCB_HV_FT_SUPPORTED);
 
 		ret = 1;
 		break;
@@ -4397,8 +4401,7 @@  int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 	case SVM_VMGEXIT_AP_CREATION:
 		ret = sev_snp_ap_creation(svm);
 		if (ret) {
-			ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_MALFORMED_INPUT);
-			ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_INPUT);
+			svm_vmgexit_bad_input(svm, GHCB_ERR_INVALID_INPUT);
 		}
 
 		ret = 1;
@@ -4635,7 +4638,7 @@  void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
 		 * Return from an AP Reset Hold VMGEXIT, where the guest will
 		 * set the CS and RIP. Set SW_EXIT_INFO_2 to a non-zero value.
 		 */
-		ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, 1);
+		svm_vmgexit_success(svm, 1);
 		break;
 	case AP_RESET_HOLD_MSR_PROTO:
 		/*
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 58bce5f1ab0c..104e13d59c8a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2977,11 +2977,7 @@  static int svm_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
 	if (!err || !sev_es_guest(vcpu->kvm) || WARN_ON_ONCE(!svm->sev_es.ghcb))
 		return kvm_complete_insn_gp(vcpu, err);
 
-	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, GHCB_HV_RESP_ISSUE_EXCEPTION);
-	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb,
-				X86_TRAP_GP |
-				SVM_EVTINJ_TYPE_EXEPT |
-				SVM_EVTINJ_VALID);
+	svm_vmgexit_inject_exception(svm, X86_TRAP_GP);
 	return 1;
 }
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 43fa6a16eb19..baff8237c5c9 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -588,6 +588,30 @@  static inline bool is_vnmi_enabled(struct vcpu_svm *svm)
 		return false;
 }
 
+static inline void svm_vmgexit_set_return_code(struct vcpu_svm *svm,
+						u64 response, u64 data)
+{
+	ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, response);
+	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, data);
+}
+
+static inline void svm_vmgexit_inject_exception(struct vcpu_svm *svm, u8 vector)
+{
+	u64 data = SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_EXEPT | vector;
+
+	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_ISSUE_EXCEPTION, data);
+}
+
+static inline void svm_vmgexit_bad_input(struct vcpu_svm *svm, u64 suberror)
+{
+	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_MALFORMED_INPUT, suberror);
+}
+
+static inline void svm_vmgexit_success(struct vcpu_svm *svm, u64 data)
+{
+	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_SUCCESS, data);
+}
+
 /* svm.c */
 #define MSR_INVALID				0xffffffffU