Re: [PATCH] xen/arm: Fix under-mapping in map_range_to_domain()

["Grall, Julien" <julien@xxxxxxx>]

Hi Michal,

Sorry for the late reply.

On 12/10/2026 08:32, Orzel, Michal wrote:
> > > I don't think we can reject unaligned regions in map_range_to_domain()
> > > though, as the host DT is not under our control and hwdom would fail to
> > > boot on platforms with sub-page devices. I asked AI to look at the Linux boards
> > > for Arm and Arm64 (140 boards in total with unaligned regions) and even the
> > > boards we claim to support have nodes that would fail:
> > > - RPI4: hdmi@7ef00700, <0x7ef01f00 0x400>
> > > - IMX8QXP: clock-controller@5b290004, <0x5b290004 0x10000>
> > I am not suggesting to reject unaligned regions when mapped into the
> > hardware domain. I am suggesting to reject it when we want to
> > passthrough to another domain. So we don't end up in a situation two
> > different devices on the same page are passthrough to two different
> > domains (or between Xen and a domain).
> >
> > Codewise, it would mean map_range_to_domain() would enforce the
> > alignment and the caller will be left to decide what to do. We could
> > also decide about the alignment base don whether this is the HW domain
> > or not within the function.
> For passthrough this is already the case. map_range_to_domain() does
> not map anything for nodes with xen,passthrough and the domU mapping is done by
> handle_passthrough_prop(), which rejects mstart, gstart and size that are not
> page aligned.
>
> The remaining case is the overlay which can be attached to any 1:1 domain and
> this goes through handle_device() -> map_range_to_domain() without any alignment
> check. All the other callers operate on hwdom, so I think we could reject a
> region that is not page aligned if d is not the hardware domain, before granting
> the iomem permission in map_range_to_domain().
>
> Shouldn't we accept this patch as is so that we can backport (overlay is not
> supported) it as a fix and then add a second one with a rejection mentioned
> above that will help the overlay (and any future) case?
Thanks for the input. I didn't realise we would want to backport this 
patch. If so, I agree the split make sense.
Acked-by: Julien Grall <julien@xxxxxxx>

Cheers,

--
Julien Grall