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

[Andrew Jones]

On Fri, May 03, 2024 at 01:39:32PM GMT, Aleksei Filippov wrote:
> 
> 
> 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.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
> 
> 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.

Legacy SBI calls like SBI_EXT_0_1_CONSOLE_GETCHAR don't return a struct
sbiret, they only return a function-specific long. The spec says for
Getchar that it returns "...the byte on success, or -1 for failure."
So we should explicitly set failure to -1, especially since
SBI_ERR_FAILURE isn't defined for legacy SBI calls.

Thanks,
drew

> -- 
> 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
> > > >