[PATCH] Trap and Emulate changes

[Anup Patel]

On Thu, Feb 12, 2026 at 9:23 PM Dave Patel <dave.patel at riscstar.com> wrote:
>
> Thanks Scott, Thanks Anup. Very much appreciated.
>
> We have already been using ecall, I can extend it to use it for paravirt for 'IRQ'.
>
> The only downside is ecall is an extension rather than trap and emulate (though it resides within trap and emulate functionality).

You don't need to define a new SBI extension for paravirt interrupt controller.

OpenSBI can emulate RPMI System MSI over SBI MPXY channel as the
paravirt interrupt controller. There are some improvements required in
the RPMI System MSI service group to achieve this which I will propose
soon.

Regards,
Anup

>
> Thanks for the feedback.
>
> Thanks and regards
> Dave
>
> On Thu, Feb 12, 2026 at 3:40 PM Anup Patel <apatel at ventanamicro.com> wrote:
>>
>> On Thu, Feb 12, 2026 at 8:38 PM Scott Bambrough <scott at riscstar.com> wrote:
>> >
>> > Is PMP universally available?
>>
>> Yes, PMP is not universally available plus we might
>> not have enough PMP regions.
>>
>> Cleaner approach is to use an "ecall" based paravirt
>> interrupt controller.
>>
>> Regards,
>> Anup
>>
>> > Scott
>> >
>> > On Thu, Feb 12, 2026 at 9:58 AM Anup Patel <apatel at ventanamicro.com> wrote:
>> >>
>> >> On Wed, Feb 11, 2026 at 3:30 PM <dave.patel at riscstar.com> wrote:
>> >> >
>> >> > From: Dave Patel <dave.patel at riscstar.com>
>> >> >
>> >> > Signed-off-by: Dave Patel <dave.patel at riscstar.com>
>> >> > ---
>> >> >  lib/sbi/sbi_illegal_insn.c | 25 ++++++++++++++++++++++++-
>> >> >  1 file changed, 24 insertions(+), 1 deletion(-)
>> >> >
>> >> > diff --git a/lib/sbi/sbi_illegal_insn.c b/lib/sbi/sbi_illegal_insn.c
>> >> > index fa82264a..88079e39 100644
>> >> > --- a/lib/sbi/sbi_illegal_insn.c
>> >> > +++ b/lib/sbi/sbi_illegal_insn.c
>> >> > @@ -110,10 +110,33 @@ static int system_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
>> >> >         return 0;
>> >> >  }
>> >> >
>> >> > +static int sbi_get_emulated_irq_insn(ulong insn, struct sbi_trap_regs *regs)
>> >> > +{
>> >> > +       ulong rs1_val   = GET_RS1(insn, regs);
>> >> > +       ulong rs2_val   = GET_RS2(insn, regs);
>> >> > +       //ulong prev_mode = sbi_mstatus_prev_mode(regs->mstatus);
>> >> > +       ulong irq_val;
>> >> > +
>> >> > +       /*
>> >> > +       // This is were the emualted irq vlaue is fetched
>> >> > +       if (prev_mode == PRV_S && sbi_emulate_irq_read(&irq_val))
>> >> > +               return truly_illegal_insn(insn, regs);
>> >> > +       */
>> >> > +
>> >> > +       // For testing
>> >> > +       irq_val = rs1_val + rs2_val;
>> >> > +
>> >> > +       SET_RD(insn, regs, irq_val);
>> >> > +
>> >> > +       regs->mepc += 4;
>> >> > +
>> >> > +       return 0;
>> >> > +}
>> >> > +
>> >> >  static const illegal_insn_func illegal_insn_table[32] = {
>> >> >         truly_illegal_insn, /* 0 */
>> >> >         truly_illegal_insn, /* 1 */
>> >> > -       truly_illegal_insn, /* 2 */
>> >> > +       sbi_get_emulated_irq_insn,   /* 2 */
>> >>
>> >> We can't pick arbitrary instruction encoding for
>> >> trap-n-emulation of an interrupt controller.
>> >>
>> >> If the goal is to trap-n-emulate an MMIO device
>> >> then use PMP based access faults.
>> >>
>> >> Regards
>> >> Anup