Re: [PATCH v3 1/3] drm/panthor: Fix IO-page mmap() for 32-bit userspace on 64-bit kernel

[Boris Brezillon <boris.brezillon@collabora.com>]

On Tue, 26 Mar 2024 12:12:03 +0100
Boris Brezillon <boris.brezillon@collabora.com> wrote:

> When mapping an IO region, the pseudo-file offset is dependent on the
> userspace architecture. panthor_device_mmio_offset() abstracts that
> away for us by turning a userspace MMIO offset into its kernel
> equivalent, but we were not updating vm_area_struct::vm_pgoff
> accordingly, leading us to attach the MMIO region to the wrong file
> offset.
> 
> This has implications when we start mixing 64 bit and 32 bit apps, but
> that's only really a problem when we start having more that 2^43 bytes of
> memory allocated, which is very unlikely to happen.
> 
> What's more problematic is the fact this turns our
> unmap_mapping_range(DRM_PANTHOR_USER_MMIO_OFFSET) calls, which are
> supposed to kill the MMIO mapping when entering suspend, into NOPs.
> Which means we either keep the dummy flush_id mapping active at all
> times, or we risk a BUS_FAULT if the MMIO region was mapped, and the
> GPU is suspended after that.
> 
> Solve that by patching vm_pgoff early in panthor_mmap(). With
> this in place, we no longer need the panthor_device_mmio_offset()
> helper.
> 
> v3:
> - No changes
> 
> v2:
> - Kill panthor_device_mmio_offset()
> 
> Fixes: 5fe909cae118 ("drm/panthor: Add the device logical block")
> Reported-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> Reported-by: Lukas F. Hartmann <lukas@mntmn.com>
> Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/10835
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> Reviewed-by: Steven Price <steven.price@arm.com>

All 3 patches queued to drm-misc-next.