Re: [PATCH v6] target/riscv/kvm/kvm-cpu.c: kvm_riscv_handle_sbi() fail with vendor-specific SBI

[Aleksei Filippov]

On 25.04.2024 12:21, Andrew Jones wrote:
On Mon, Apr 22, 2024 at 02:31:36PM +0200, Andrew Jones wrote:
On Mon, Apr 22, 2024 at 02:42:54PM +0300, Alexei Filippov wrote:
kvm_riscv_handle_sbi() may return not supported return code to not
trigger qemu abort with vendor-specific sbi.

Add new error path to provide proper error in case of
qemu_chr_fe_read_all() may not return sizeof(ch).

I think something more along the lines of what I wrote in my previous
reply will help clarify this more. Here's what I wrote

"""
Exactly zero just means we failed to read input, which can happen, so
telling the SBI caller we failed to read, but telling the caller of this
function that we successfully emulated the SBI call, is correct. However,
anything else, other than sizeof(ch), means something unexpected happened,
so we should indeed return an error from this function.
"""

Thanks,
drew


Added SBI related return code's defines.

Signed-off-by: Alexei Filippov <alexei.filip...@syntacore.com>
---
Changes since v4-5:
                -Added new error path in case of qemu_chr_fe_read_all() may not
                return sizeof(ch).
                -Added more comments in commit message.
  target/riscv/kvm/kvm-cpu.c         | 10 ++++++----
  target/riscv/sbi_ecall_interface.h | 12 ++++++++++++
  2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index f9dbc18a76..5bb7b74d03 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -1173,16 +1173,18 @@ static int kvm_riscv_handle_sbi(CPUState *cs, struct 
kvm_run *run)
          ret = qemu_chr_fe_read_all(serial_hd(0)->be, &ch, sizeof(ch));
          if (ret == sizeof(ch)) {
              run->riscv_sbi.ret[0] = ch;
+            ret = 0;
+        } else if (ret == 0) {
+            run->riscv_sbi.ret[0] = SBI_ERR_FAILURE;

I'd prefer we still explicitly assign ret[0] to -1 here since that's what
the spec explicitly says.

Thanks,
drew

Can you please explain it a little bit more, cz I believe SBI_ERR_FAILURE is -1 
anyway. Defines was added at first place just to came along with Linux kernel 
SBI related defines.
--
Sincerely,
Aleksei Filippov

          } else {
-            run->riscv_sbi.ret[0] = -1;
+            ret = -1;
          }
-        ret = 0;
          break;
      default:
          qemu_log_mask(LOG_UNIMP,
-                      "%s: un-handled SBI EXIT, specific reasons is %lu\n",
+                      "%s: Unhandled SBI exit with extension-id %lu\n"
                        __func__, run->riscv_sbi.extension_id);
-        ret = -1;
+        run->riscv_sbi.ret[0] = SBI_ERR_NOT_SUPPORTED;
          break;
      }
      return ret;
diff --git a/target/riscv/sbi_ecall_interface.h 
b/target/riscv/sbi_ecall_interface.h
index 43899d08f6..a2e21d9b8c 100644
--- a/target/riscv/sbi_ecall_interface.h
+++ b/target/riscv/sbi_ecall_interface.h
@@ -69,4 +69,16 @@
  #define SBI_EXT_VENDOR_END              0x09FFFFFF
  /* clang-format on */
  
+/* SBI return error codes */
+#define SBI_SUCCESS                  0
+#define SBI_ERR_FAILURE             -1
+#define SBI_ERR_NOT_SUPPORTED       -2
+#define SBI_ERR_INVALID_PARAM       -3
+#define SBI_ERR_DENIED              -4
+#define SBI_ERR_INVALID_ADDRESS     -5
+#define SBI_ERR_ALREADY_AVAILABLE   -6
+#define SBI_ERR_ALREADY_STARTED     -7
+#define SBI_ERR_ALREADY_STOPPED     -8
+#define SBI_ERR_NO_SHMEM            -9
+
  #endif
--
2.34.1