drm/panthor: Fix IO-page mmap() for 32-bit userspace on 64-bit kernel

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>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240326111205.510019-1-boris.brezillon@collabora.com

1 files changed, 16 insertions, 1 deletions

diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
index 11b3ccd58f85..730dd0c69cb8 100644
--- a/drivers/gpu/drm/panthor/panthor_drv.c
+++ b/drivers/gpu/drm/panthor/panthor_drv.c
@@ -1327,7 +1327,22 @@ static int panthor_mmap(struct file *filp, struct vm_area_struct *vma)
 	if (!drm_dev_enter(file->minor->dev, &cookie))
 		return -ENODEV;
 
-	if (panthor_device_mmio_offset(offset) >= DRM_PANTHOR_USER_MMIO_OFFSET)
+#ifdef CONFIG_ARM64
+	/*
+	 * With 32-bit systems being limited by the 32-bit representation of
+	 * mmap2's pgoffset field, we need to make the MMIO offset arch
+	 * specific. This converts a user MMIO offset into something the kernel
+	 * driver understands.
+	 */
+	if (test_tsk_thread_flag(current, TIF_32BIT) &&
+	    offset >= DRM_PANTHOR_USER_MMIO_OFFSET_32BIT) {
+		offset += DRM_PANTHOR_USER_MMIO_OFFSET_64BIT -
+			  DRM_PANTHOR_USER_MMIO_OFFSET_32BIT;
+		vma->vm_pgoff = offset >> PAGE_SHIFT;
+	}
+#endif
+
+	if (offset >= DRM_PANTHOR_USER_MMIO_OFFSET)
 		ret = panthor_device_mmap_io(ptdev, vma);
 	else
 		ret = drm_gem_mmap(filp, vma);