RISC-V: KVM: Modify SBI extension handler to return SBI error code

Currently, the SBI extension handle is expected to return Linux error code.
The top SBI layer converts the Linux error code to SBI specific error code
that can be returned to guest invoking the SBI calls. This model works
as long as SBI error codes have 1-to-1 mappings between them.
However, that may not be true always. This patch attempts to disassociate
both these error codes by allowing the SBI extension implementation to
return SBI specific error codes as well.

The extension will continue to return the Linux error specific code which
will indicate any problem *with* the extension emulation while the
SBI specific error will indicate the problem *of* the emulation.

Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

arch/riscv/include/asm/kvm_vcpu_sbi.h

@@ -18,6 +18,13 @@ struct kvm_vcpu_sbi_context {
 	int return_handled;
 };
 
+struct kvm_vcpu_sbi_return {
+	unsigned long out_val;
+	unsigned long err_val;
+	struct kvm_cpu_trap *utrap;
+	bool uexit;
+};
+
 struct kvm_vcpu_sbi_extension {
 	unsigned long extid_start;
 	unsigned long extid_end;
@@ -27,8 +34,7 @@ struct kvm_vcpu_sbi_extension {
 	 * specific error codes.
 	 */
 	int (*handler)(struct kvm_vcpu *vcpu, struct kvm_run *run,
-		       unsigned long *out_val, struct kvm_cpu_trap *utrap,
-		       bool *exit);
+		       struct kvm_vcpu_sbi_return *retdata);
 
 	/* Extension specific probe function */
 	unsigned long (*probe)(struct kvm_vcpu *vcpu);

arch/riscv/kvm/vcpu_sbi.c

@@ -12,26 +12,6 @@
 #include <asm/sbi.h>
 #include <asm/kvm_vcpu_sbi.h>
 
-static int kvm_linux_err_map_sbi(int err)
-{
-	switch (err) {
-	case 0:
-		return SBI_SUCCESS;
-	case -EPERM:
-		return SBI_ERR_DENIED;
-	case -EINVAL:
-		return SBI_ERR_INVALID_PARAM;
-	case -EFAULT:
-		return SBI_ERR_INVALID_ADDRESS;
-	case -EOPNOTSUPP:
-		return SBI_ERR_NOT_SUPPORTED;
-	case -EALREADY:
-		return SBI_ERR_ALREADY_AVAILABLE;
-	default:
-		return SBI_ERR_FAILURE;
-	};
-}
-
 #ifndef CONFIG_RISCV_SBI_V01
 static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_v01 = {
 	.extid_start = -1UL,
@@ -125,11 +105,14 @@ int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
 	int ret = 1;
 	bool next_sepc = true;
-	bool userspace_exit = false;
 	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
 	const struct kvm_vcpu_sbi_extension *sbi_ext;
 	struct kvm_cpu_trap utrap = {0};
-	unsigned long out_val = 0;
+	struct kvm_vcpu_sbi_return sbi_ret = {
+		.out_val = 0,
+		.err_val = 0,
+		.utrap = &utrap,
+	};
 	bool ext_is_v01 = false;
 
 	sbi_ext = kvm_vcpu_sbi_find_ext(cp->a7);
@@ -139,42 +122,46 @@ int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		    cp->a7 <= SBI_EXT_0_1_SHUTDOWN)
 			ext_is_v01 = true;
 #endif
-		ret = sbi_ext->handler(vcpu, run, &out_val, &utrap, &userspace_exit);
+		ret = sbi_ext->handler(vcpu, run, &sbi_ret);
 	} else {
 		/* Return error for unsupported SBI calls */
 		cp->a0 = SBI_ERR_NOT_SUPPORTED;
 		goto ecall_done;
 	}
 
+	/*
+	 * When the SBI extension returns a Linux error code, it exits the ioctl
+	 * loop and forwards the error to userspace.
+	 */
+	if (ret < 0) {
+		next_sepc = false;
+		goto ecall_done;
+	}
+
 	/* Handle special error cases i.e trap, exit or userspace forward */
-	if (utrap.scause) {
+	if (sbi_ret.utrap->scause) {
 		/* No need to increment sepc or exit ioctl loop */
 		ret = 1;
-		utrap.sepc = cp->sepc;
-		kvm_riscv_vcpu_trap_redirect(vcpu, &utrap);
+		sbi_ret.utrap->sepc = cp->sepc;
+		kvm_riscv_vcpu_trap_redirect(vcpu, sbi_ret.utrap);
 		next_sepc = false;
 		goto ecall_done;
 	}
 
 	/* Exit ioctl loop or Propagate the error code the guest */
-	if (userspace_exit) {
+	if (sbi_ret.uexit) {
 		next_sepc = false;
 		ret = 0;
 	} else {
-		/**
-		 * SBI extension handler always returns an Linux error code. Convert
-		 * it to the SBI specific error code that can be propagated the SBI
-		 * caller.
-		 */
-		ret = kvm_linux_err_map_sbi(ret);
-		cp->a0 = ret;
+		cp->a0 = sbi_ret.err_val;
 		ret = 1;
 	}
 ecall_done:
 	if (next_sepc)
 		cp->sepc += 4;
-	if (!ext_is_v01)
-		cp->a1 = out_val;
+	/* a1 should only be updated when we continue the ioctl loop */
+	if (!ext_is_v01 && ret == 1)
+		cp->a1 = sbi_ret.out_val;
 
 	return ret;
 }

arch/riscv/kvm/vcpu_sbi_base.c

@@ -14,12 +14,11 @@
 #include <asm/kvm_vcpu_sbi.h>
 
 static int kvm_sbi_ext_base_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
-				    unsigned long *out_val,
-				    struct kvm_cpu_trap *trap, bool *exit)
+				    struct kvm_vcpu_sbi_return *retdata)
 {
-	int ret = 0;
 	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
 	const struct kvm_vcpu_sbi_extension *sbi_ext;
+	unsigned long *out_val = &retdata->out_val;
 
 	switch (cp->a6) {
 	case SBI_EXT_BASE_GET_SPEC_VERSION:
@@ -43,7 +42,7 @@ static int kvm_sbi_ext_base_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 			 * forward it to the userspace
 			 */
 			kvm_riscv_vcpu_sbi_forward(vcpu, run);
-			*exit = true;
+			retdata->uexit = true;
 		} else {
 			sbi_ext = kvm_vcpu_sbi_find_ext(cp->a0);
 			*out_val = sbi_ext && sbi_ext->probe ?
@@ -60,11 +59,11 @@ static int kvm_sbi_ext_base_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		*out_val = vcpu->arch.mimpid;
 		break;
 	default:
-		ret = -EOPNOTSUPP;
+		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
 		break;
 	}
 
-	return ret;
+	return 0;
 }
 
 const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_base = {
@@ -75,16 +74,14 @@ const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_base = {
 
 static int kvm_sbi_ext_forward_handler(struct kvm_vcpu *vcpu,
 				       struct kvm_run *run,
-					unsigned long *out_val,
-					struct kvm_cpu_trap *utrap,
-					bool *exit)
+				       struct kvm_vcpu_sbi_return *retdata)
 {
 	/*
 	 * Both SBI experimental and vendor extensions are
 	 * unconditionally forwarded to userspace.
 	 */
 	kvm_riscv_vcpu_sbi_forward(vcpu, run);
-	*exit = true;
+	retdata->uexit = true;
 	return 0;
 }
 

arch/riscv/kvm/vcpu_sbi_hsm.c

@@ -21,9 +21,9 @@ static int kvm_sbi_hsm_vcpu_start(struct kvm_vcpu *vcpu)
 
 	target_vcpu = kvm_get_vcpu_by_id(vcpu->kvm, target_vcpuid);
 	if (!target_vcpu)
-		return -EINVAL;
+		return SBI_ERR_INVALID_PARAM;
 	if (!target_vcpu->arch.power_off)
-		return -EALREADY;
+		return SBI_ERR_ALREADY_AVAILABLE;
 
 	reset_cntx = &target_vcpu->arch.guest_reset_context;
 	/* start address */
@@ -42,7 +42,7 @@ static int kvm_sbi_hsm_vcpu_start(struct kvm_vcpu *vcpu)
 static int kvm_sbi_hsm_vcpu_stop(struct kvm_vcpu *vcpu)
 {
 	if (vcpu->arch.power_off)
-		return -EACCES;
+		return SBI_ERR_FAILURE;
 
 	kvm_riscv_vcpu_power_off(vcpu);
 
@@ -57,7 +57,7 @@ static int kvm_sbi_hsm_vcpu_get_status(struct kvm_vcpu *vcpu)
 
 	target_vcpu = kvm_get_vcpu_by_id(vcpu->kvm, target_vcpuid);
 	if (!target_vcpu)
-		return -EINVAL;
+		return SBI_ERR_INVALID_PARAM;
 	if (!target_vcpu->arch.power_off)
 		return SBI_HSM_STATE_STARTED;
 	else if (vcpu->stat.generic.blocking)
@@ -67,9 +67,7 @@ static int kvm_sbi_hsm_vcpu_get_status(struct kvm_vcpu *vcpu)
 }
 
 static int kvm_sbi_ext_hsm_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
-				   unsigned long *out_val,
-				   struct kvm_cpu_trap *utrap,
-				   bool *exit)
+				   struct kvm_vcpu_sbi_return *retdata)
 {
 	int ret = 0;
 	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
@@ -88,27 +86,29 @@ static int kvm_sbi_ext_hsm_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	case SBI_EXT_HSM_HART_STATUS:
 		ret = kvm_sbi_hsm_vcpu_get_status(vcpu);
 		if (ret >= 0) {
-			*out_val = ret;
-			ret = 0;
+			retdata->out_val = ret;
+			retdata->err_val = 0;
 		}
-		break;
+		return 0;
 	case SBI_EXT_HSM_HART_SUSPEND:
 		switch (cp->a0) {
 		case SBI_HSM_SUSPEND_RET_DEFAULT:
 			kvm_riscv_vcpu_wfi(vcpu);
 			break;
 		case SBI_HSM_SUSPEND_NON_RET_DEFAULT:
-			ret = -EOPNOTSUPP;
+			ret = SBI_ERR_NOT_SUPPORTED;
 			break;
 		default:
-			ret = -EINVAL;
+			ret = SBI_ERR_INVALID_PARAM;
 		}
 		break;
 	default:
-		ret = -EOPNOTSUPP;
+		ret = SBI_ERR_NOT_SUPPORTED;
 	}
 
-	return ret;
+	retdata->err_val = ret;
+
+	return 0;
 }
 
 const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm = {

arch/riscv/kvm/vcpu_sbi_replace.c

@@ -14,15 +14,15 @@
 #include <asm/kvm_vcpu_sbi.h>
 
 static int kvm_sbi_ext_time_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
-				    unsigned long *out_val,
-				    struct kvm_cpu_trap *utrap, bool *exit)
+				    struct kvm_vcpu_sbi_return *retdata)
 {
-	int ret = 0;
 	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
 	u64 next_cycle;
 
-	if (cp->a6 != SBI_EXT_TIME_SET_TIMER)
-		return -EINVAL;
+	if (cp->a6 != SBI_EXT_TIME_SET_TIMER) {
+		retdata->err_val = SBI_ERR_INVALID_PARAM;
+		return 0;
+	}
 
 #if __riscv_xlen == 32
 	next_cycle = ((u64)cp->a1 << 32) | (u64)cp->a0;
@@ -31,7 +31,7 @@ static int kvm_sbi_ext_time_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 #endif
 	kvm_riscv_vcpu_timer_next_event(vcpu, next_cycle);
 
-	return ret;
+	return 0;
 }
 
 const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_time = {
@@ -41,8 +41,7 @@ const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_time = {
 };
 
 static int kvm_sbi_ext_ipi_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
-				   unsigned long *out_val,
-				   struct kvm_cpu_trap *utrap, bool *exit)
+				   struct kvm_vcpu_sbi_return *retdata)
 {
 	int ret = 0;
 	unsigned long i;
@@ -51,8 +50,10 @@ static int kvm_sbi_ext_ipi_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	unsigned long hmask = cp->a0;
 	unsigned long hbase = cp->a1;
 
-	if (cp->a6 != SBI_EXT_IPI_SEND_IPI)
-		return -EINVAL;
+	if (cp->a6 != SBI_EXT_IPI_SEND_IPI) {
+		retdata->err_val = SBI_ERR_INVALID_PARAM;
+		return 0;
+	}
 
 	kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
 		if (hbase != -1UL) {
@@ -76,10 +77,8 @@ const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_ipi = {
 };
 
 static int kvm_sbi_ext_rfence_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
-				      unsigned long *out_val,
-				      struct kvm_cpu_trap *utrap, bool *exit)
+				      struct kvm_vcpu_sbi_return *retdata)
 {
-	int ret = 0;
 	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
 	unsigned long hmask = cp->a0;
 	unsigned long hbase = cp->a1;
@@ -116,10 +115,10 @@ static int kvm_sbi_ext_rfence_handler(struct kvm_vcpu *vcpu, struct kvm_run *run
 		 */
 		break;
 	default:
-		ret = -EOPNOTSUPP;
+		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
 	}
 
-	return ret;
+	return 0;
 }
 
 const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_rfence = {
@@ -130,14 +129,12 @@ const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_rfence = {
 
 static int kvm_sbi_ext_srst_handler(struct kvm_vcpu *vcpu,
 				    struct kvm_run *run,
-				    unsigned long *out_val,
-				    struct kvm_cpu_trap *utrap, bool *exit)
+				    struct kvm_vcpu_sbi_return *retdata)
 {
 	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
 	unsigned long funcid = cp->a6;
 	u32 reason = cp->a1;
 	u32 type = cp->a0;
-	int ret = 0;
 
 	switch (funcid) {
 	case SBI_EXT_SRST_RESET:
@@ -146,24 +143,24 @@ static int kvm_sbi_ext_srst_handler(struct kvm_vcpu *vcpu,
 			kvm_riscv_vcpu_sbi_system_reset(vcpu, run,
 						KVM_SYSTEM_EVENT_SHUTDOWN,
 						reason);
-			*exit = true;
+			retdata->uexit = true;
 			break;
 		case SBI_SRST_RESET_TYPE_COLD_REBOOT:
 		case SBI_SRST_RESET_TYPE_WARM_REBOOT:
 			kvm_riscv_vcpu_sbi_system_reset(vcpu, run,
 						KVM_SYSTEM_EVENT_RESET,
 						reason);
-			*exit = true;
+			retdata->uexit = true;
 			break;
 		default:
-			ret = -EOPNOTSUPP;
+			retdata->err_val = SBI_ERR_NOT_SUPPORTED;
 		}
 		break;
 	default:
-		ret = -EOPNOTSUPP;
+		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
 	}
 
-	return ret;
+	return 0;
 }
 
 const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_srst = {

arch/riscv/kvm/vcpu_sbi_v01.c

@@ -14,9 +14,7 @@
 #include <asm/kvm_vcpu_sbi.h>
 
 static int kvm_sbi_ext_v01_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
-				      unsigned long *out_val,
-				      struct kvm_cpu_trap *utrap,
-				      bool *exit)
+				   struct kvm_vcpu_sbi_return *retdata)
 {
 	ulong hmask;
 	int i, ret = 0;
@@ -24,6 +22,7 @@ static int kvm_sbi_ext_v01_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	struct kvm_vcpu *rvcpu;
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	struct kvm_cpu_trap *utrap = retdata->utrap;
 
 	switch (cp->a7) {
 	case SBI_EXT_0_1_CONSOLE_GETCHAR:
@@ -33,7 +32,7 @@ static int kvm_sbi_ext_v01_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		 * handled in kernel so we forward these to user-space
 		 */
 		kvm_riscv_vcpu_sbi_forward(vcpu, run);
-		*exit = true;
+		retdata->uexit = true;
 		break;
 	case SBI_EXT_0_1_SET_TIMER:
 #if __riscv_xlen == 32
@@ -48,8 +47,7 @@ static int kvm_sbi_ext_v01_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		break;
 	case SBI_EXT_0_1_SEND_IPI:
 		if (cp->a0)
-			hmask = kvm_riscv_vcpu_unpriv_read(vcpu, false, cp->a0,
-							   utrap);
+			hmask = kvm_riscv_vcpu_unpriv_read(vcpu, false, cp->a0, utrap);
 		else
 			hmask = (1UL << atomic_read(&kvm->online_vcpus)) - 1;
 		if (utrap->scause)
@@ -65,14 +63,13 @@ static int kvm_sbi_ext_v01_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	case SBI_EXT_0_1_SHUTDOWN:
 		kvm_riscv_vcpu_sbi_system_reset(vcpu, run,
 						KVM_SYSTEM_EVENT_SHUTDOWN, 0);
-		*exit = true;
+		retdata->uexit = true;
 		break;
 	case SBI_EXT_0_1_REMOTE_FENCE_I:
 	case SBI_EXT_0_1_REMOTE_SFENCE_VMA:
 	case SBI_EXT_0_1_REMOTE_SFENCE_VMA_ASID:
 		if (cp->a0)
-			hmask = kvm_riscv_vcpu_unpriv_read(vcpu, false, cp->a0,
-							   utrap);
+			hmask = kvm_riscv_vcpu_unpriv_read(vcpu, false, cp->a0, utrap);
 		else
 			hmask = (1UL << atomic_read(&kvm->online_vcpus)) - 1;
 		if (utrap->scause)
@@ -103,7 +100,7 @@ static int kvm_sbi_ext_v01_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		}
 		break;
 	default:
-		ret = -EINVAL;
+		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
 		break;
 	}