Re: [PATCH v3 06/23] xen/riscv: introduce guest riscv,isa string

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.06.2026 13:17, Oleksii Kurochko wrote:
> Introduce generation of the riscv,isa string passed to the guest via the
> Device Tree riscv,isa property.
> 
> Introduce the per-domain isa string and guest isa bitmap, populated
> during domain creation by calling init_guest_isa().
> 
> Introduce guest_unsupp to filter out ISA extensions that should not be
> exposed to guests:
> 
> - f/d/q/v: FPU and vector context save/restore are not yet implemented
>   for guests.

I may have asked before - what about Zfinx, Zdinx (and the supposed Zqinx)?
They aren't in riscv_isa_ext[], yes, but perhaps wrongly so? And hence they
may want at least mentioning?

> @@ -480,6 +489,78 @@ bool riscv_isa_extension_available(const unsigned long 
> *isa_bitmap,
>      return test_bit(id, isa_bitmap);
>  }
>  
> +static int build_guest_isa_str(char *buf, size_t size,
> +                               const unsigned long *isa_bitmap)
> +{
> +    int total;
> +
> +#if defined(CONFIG_RISCV_32)
> +    total = snprintf(buf, size, "rv32");
> +#elif defined(CONFIG_RISCV_64)
> +    total = snprintf(buf, size, "rv64");
> +#else
> +#   error "Unsupported RISC-V bitness"
> +#endif
> +
> +    if ( total < 0 )
> +        return total;
> +
> +    for ( unsigned int i = 0; i < ARRAY_SIZE(riscv_isa_ext); i++ )
> +    {
> +        const struct riscv_isa_ext_data *ext = &riscv_isa_ext[i];
> +        int ret;
> +
> +        if ( !riscv_isa_extension_available(isa_bitmap, ext->id) )
> +            continue;
> +
> +        ret = snprintf(buf ? buf + total : NULL,
> +                       buf ? size - total : 0, "%s%s",

If total > size this subtraction will underflow and a huge value will be
passed to snprintf().

Jan