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

From: Boris Brezillon <boris.brezillon@collabora.com>
To: "Boris Brezillon" <boris.brezillon@collabora.com>,
	"Steven Price" <steven.price@arm.com>,
	"Liviu Dudau" <liviu.dudau@arm.com>,
	"Adrián Larumbe" <adrian.larumbe@collabora.com>
Cc: dri-devel@lists.freedesktop.org, kernel@collabora.com,
	"Lukas F . Hartmann" <lukas@mntmn.com>
Subject: Re: [PATCH v3 1/3] drm/panthor: Fix IO-page mmap() for 32-bit userspace on 64-bit kernel
Date: Tue, 2 Apr 2024 09:36:35 +0200	[thread overview]
Message-ID: <20240402093635.056bd8dc@collabora.com> (raw)
In-Reply-To: <20240326111205.510019-1-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.