[PATCH 3/3] drm/panthor: Move cache-flush after UPDATE(UNMAPPED)

[Boris Brezillon]

Right now, there's a theoretical window during which the GPU can populate
the cache with data from a VM that's about to be evicted through the
UPDATE(UNMAPPED) command.
In practice this won't happen (hence the absence of Fixes tag) because
when panthor_mmu_as_disable() is called, the VM is guaranteed to be idle
(no active CSG pointing to this VM), but as we say, better safe than
sorry.

Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/panthor/panthor_mmu.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
index 038a092fd08c..bb71274aa36b 100644
--- a/drivers/gpu/drm/panthor/panthor_mmu.c
+++ b/drivers/gpu/drm/panthor/panthor_mmu.c
@@ -631,12 +631,6 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr)
 	panthor_mmu_irq_disable_events(&ptdev->mmu->irq,
 				       panthor_mmu_as_fault_mask(ptdev, as_nr));
 
-	/* Flush+invalidate RW caches, invalidate RO ones. */
-	ret = panthor_gpu_flush_caches(ptdev, CACHE_CLEAN | CACHE_INV,
-				       CACHE_CLEAN | CACHE_INV, 0);
-	if (ret)
-		return ret;
-
 	if (vm && vm->locked_region.size) {
 		/* Unlock the region if there's a lock pending. */
 		ret = as_send_cmd_and_wait(ptdev, vm->as.id, AS_COMMAND_UNLOCK);
@@ -648,7 +642,18 @@ static int panthor_mmu_as_disable(struct panthor_device *ptdev, u32 as_nr)
 	gpu_write64(mmu->iomem, AS_MEMATTR(as_nr), 0);
 	gpu_write64(mmu->iomem, AS_TRANSCFG(as_nr), AS_TRANSCFG_ADRMODE_UNMAPPED);
 
-	return as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_UPDATE);
+	ret = as_send_cmd_and_wait(ptdev, as_nr, AS_COMMAND_UPDATE);
+	if (ret)
+		return ret;
+
+	/* Flush+invalidate RW caches after we've unmapped, to make sure any
+	 * cacheline eviction is effective before we potentially return
+	 * memory pointed by this VM to the system. This needs to be done
+	 * after the UPDATE(UNMAPPED) operation to guarantee that not further
+	 * PT-walk can pull VM data into the cache.
+	 */
+	return panthor_gpu_flush_caches(ptdev, CACHE_CLEAN | CACHE_INV,
+					CACHE_CLEAN | CACHE_INV, 0);
 }
 
 static u32 panthor_mmu_fault_mask(struct panthor_device *ptdev, u32 value)

-- 
2.55.0