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>

1 files changed, 24 insertions, 37 deletions

diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index f96991d230bf..fe2897e3fde1 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/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_cpu_trap utrap = {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;
 }