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

[Andrew Jones]

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.filippov@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

> >          } 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
> >