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

[Jan Beulich <jbeulich@xxxxxxxx>]

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?

> --- /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.

Jan