Re: [PATCH v9] target/riscv/kvm/kvm-cpu.c: kvm_riscv_handle_sbi() fail with vendor-specific SBI

[Andrew Jones]

On Tue, Sep 17, 2024 at 02:54:33PM 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")

Fixes tag goes above s-o-b and 8 hex digits is a bit small. Most
commit references in QEMU are using 10 or 12 digits.

> ---
>  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 f6e3156b8d..9f2ca67c9f 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -1517,19 +1517,21 @@ 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;

Looks good!

>          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;

This, along with the addition of the SBI_* defines below, should be a
separate patch. If we were just naming the -1, then I wouldn't mind it
slipping in with the same patch, but this is changing behavior since
SBI_ERR_NOT_SUPPORTED is -2. I agree with the change, though, it just
needs to be a separate patch. And the separate patch should have the
same Fixes tag.

Thanks,
drew

>          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
>