Re: [PATCH v3 3/3] xen/riscv: add RISC-V virtual SBI base extension support for guests

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 12/23/25 5:13 PM, Jan Beulich wrote:
> On 22.12.2025 17:37, Oleksii Kurochko wrote:
> > --- a/xen/arch/riscv/include/asm/sbi.h
> > +++ b/xen/arch/riscv/include/asm/sbi.h
> > @@ -14,6 +14,13 @@
> >   
> >   #include <xen/cpumask.h>
> >   
> > +/* Xen-controlled SBI version reported to guests */
> > +#define XEN_SBI_VER_MAJOR 0
> > +#define XEN_SBI_VER_MINOR 2
> Are these going to gain a 2nd use, justifying their placement here?
Good point. I don't have any plans now to use them somewhere else, so,
at least, for now it would be really put them to base-extension.c.

> > --- /dev/null
> > +++ b/xen/arch/riscv/vsbi/base-extension.c
> > @@ -0,0 +1,78 @@
> > +
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <xen/lib.h>
> > +#include <xen/sched.h>
> > +#include <xen/version.h>
> > +
> > +#include <asm/processor.h>
> > +#include <asm/sbi.h>
> > +#include <asm/vsbi.h>
> > +
> > +static int vsbi_base_ecall_handler(unsigned long eid, unsigned long fid,
> > +                                   struct cpu_user_regs *regs)
> > +{
> > +    int ret = 0;
> > +    struct sbiret sbi_ret;
> > +
> > +    ASSERT(eid == SBI_EXT_BASE);
> > +
> > +    switch ( fid )
> > +    {
> > +    case SBI_EXT_BASE_GET_SPEC_VERSION:
> > +        regs->a1 = MASK_INSR(XEN_SBI_VER_MAJOR, SBI_SPEC_VERSION_MAJOR_MASK) |
> > +                   XEN_SBI_VER_MINOR;
> > +        break;
> > +
> > +    case SBI_EXT_BASE_GET_IMP_ID:
> > +        regs->a1 = SBI_XEN_IMPID;
> > +        break;
> > +
> > +    case SBI_EXT_BASE_GET_IMP_VERSION:
> > +        regs->a1 = (xen_major_version() << 16) | xen_minor_version();
> > +        break;
> > +
> > +    case SBI_EXT_BASE_GET_MVENDORID:
> > +    case SBI_EXT_BASE_GET_MARCHID:
> > +    case SBI_EXT_BASE_GET_MIMPID:
> > +        if ( is_hardware_domain(current->domain) )
> > +        {
> > +            sbi_ret = sbi_ecall(SBI_EXT_BASE, fid, 0, 0, 0, 0, 0, 0);
> > +            ret = sbi_ret.error;
> > +            regs->a1 = sbi_ret.value;
> > +        }
> > +        else
> > +            /*
> > +             * vSBI should present a consistent, virtualized view to guests.
> > +             * In particular, DomU-visible data must remain stable across
> > +             * migration and must not expose hardware-specific details.
> > +             *
> > +             * These register(s) must be readable in any implementation,
> > +             * but a value of 0 can be returned to indicate the field
> > +             * is not implemented.
> > +             */
> > +            regs->a1 = 0;
> > +
> > +        break;
> > +
> > +    case SBI_EXT_BASE_PROBE_EXT:
> > +        regs->a1 = vsbi_find_extension(regs->a0) ? 1 : 0;
> > +        break;
> > +
> > +    default:
> > +        /*
> > +         * TODO: domain_crash() is acceptable here while things are still under
> > +         * development.
> > +         * It shouldn't stay like this in the end though: guests should not
> > +         * be punished like this for something Xen hasn't implemented.
> > +         */
> > +        domain_crash(current->domain,
> > +                     "%s: Unsupported ecall: FID: #%lx, EID: #%lx\n",
> Same remark here as for patch 2.
I'll update to #%lu for FID.

Thanks.

~ Oleksii