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 02:29:41PM GMT, Andrew Jones wrote:
> 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.
>

Actually it's even more of a difference than s/-1/-2/ since we're no long
aborting the SBI call, but returning non-supported instead.

Thanks,
drew