Re: [PATCH v8] target/riscv/kvm/kvm-cpu.c: kvm_riscv_handle_sbi() fail with vendor-specific SBI

[Andrew Jones]

On Tue, Jun 25, 2024 at 06:02:54PM GMT, 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), because 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 return an error.
> 
> Added SBI related return code's defines.
> 
> Signed-off-by: Alexei Filippov <alexei.filippov@syntacore.com>
> Fixes: 4eb47125 ("target/riscv: Handle KVM_EXIT_RISCV_SBI exit")
> ---
> Changes since v7:
>               - Fix error handling according to Andrew Jones suggestion.
>  target/riscv/kvm/kvm-cpu.c         |  9 +++++----
>  target/riscv/sbi_ecall_interface.h | 12 ++++++++++++
>  2 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index 235e2cdaca..1afbabe19f 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -1515,19 +1515,20 @@ 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;
> +        } else if (ret == 0) {
> +            run->riscv_sbi.ret[0] = SBI_ERR_FAILURE;
>          } else {
> -            run->riscv_sbi.ret[0] = -1;
> +            ret = -1;
>          }
> -        ret = 0;

It should be

diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
index 235e2cdaca1a..9946afb4eade 100644
--- a/target/riscv/kvm/kvm-cpu.c
+++ b/target/riscv/kvm/kvm-cpu.c
@@ -1515,10 +1515,12 @@ 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;
-        } else {
+            ret = 0;
+        } else if (ret == 0) {
             run->riscv_sbi.ret[0] = -1;
+        } else {
+            ret = -1;
         }
-        ret = 0;
         break;
     case SBI_EXT_DBCN:
         kvm_riscv_handle_sbi_dbcn(cs, run);

I misled you on that first 'ret = 0' addition, we need that, but I've
pointed out a few times that we should use '-1' instead of SBI_ERR_FAILURE
and why.

Thanks,
drew

>          break;
>      case SBI_EXT_DBCN:
>          kvm_riscv_handle_sbi_dbcn(cs, run);
>          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 7dfe5f72c6..4df0accd78 100644
> --- a/target/riscv/sbi_ecall_interface.h
> +++ b/target/riscv/sbi_ecall_interface.h
> @@ -86,4 +86,16 @@
>  #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
>