[PATCH 1/2] lib: sbi_domain: Allow MMIO access to non-MMIO ranges

[Anup Patel]

On Sat, Nov 22, 2025 at 1:08 AM Samuel Holland
<samuel.holland at sifive.com> wrote:
>
> Currently, platforms do not provide complete memory region information
> to OpenSBI. Generally, memory regions are only created for the few MMIO
> devices that have M-mode drivers. As a result, most MMIO devices fall
> inside the default S-mode RWX memory region, which does _not_ have the
> MMIO flag set.
>
> In fact, OpenSBI relies on certain S-mode MMIO devices being inside
> non-MMIO memory regions. Both fdt_domain_based_fixup_one() and
> mpxy_rpmi_sysmis_xfer() call sbi_domain_check_addr() with the MMIO flag
> cleared, and that function currently requires an exact flag match. Those
> access checks will thus erroneously fail if the platform creates memory
> regions with the correct flags for these devices (or for a larger MMIO
> region containing these devices).
>
> We should not ignore the MMIO flag entirely, because
> sbi_domain_check_addr() is also used to check the permissions of S-mode
> shared memory buffers, and S-mode should not be using MMIO device
> addresses as memory buffers. But when checking if S-mode is allowed to
> do MMIO accesses, we need to recognize that MMIO devices appear in
> memory regions both with and without the MMIO flag set.
>
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>

LGTM.

Reviewed-by: Anup Patel <anup at brainfault.org>

Applied this patch to the riscv/opensbi repo.

Thanks,
Anup

> ---
>
>  lib/sbi/sbi_domain.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/lib/sbi/sbi_domain.c b/lib/sbi/sbi_domain.c
> index da0f0557..0da43d76 100644
> --- a/lib/sbi/sbi_domain.c
> +++ b/lib/sbi/sbi_domain.c
> @@ -236,7 +236,11 @@ bool sbi_domain_check_addr(const struct sbi_domain *dom,
>                         rstart + ((1UL << reg->order) - 1) : -1UL;
>                 if (rstart <= addr && addr <= rend) {
>                         rmmio = (rflags & SBI_DOMAIN_MEMREGION_MMIO) ? true : false;
> -                       if (mmio != rmmio)
> +                       /*
> +                        * MMIO devices may appear in regions without the flag set (such as the
> +                        * default region), but MMIO device regions should not be used as memory.
> +                        */
> +                       if (!mmio && rmmio)
>                                 return false;
>                         return ((rrwx & rwx) == rwx) ? true : false;
>                 }
> --
> 2.47.2
>
>
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