[PATCH v3 03/33] iommu/io-pgtable-arm: Add quirk to quiet WARN_ON()

[Rob Clark <robdclark@gmail.com>]

From: Rob Clark <robdclark@chromium.org>

In situations where mapping/unmapping squence can be controlled by
userspace, attempting to map over a region that has not yet been
unmapped is an error.  But not something that should spam dmesg.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/iommu/io-pgtable-arm.c | 18 ++++++++++++------
 include/linux/io-pgtable.h     |  8 ++++++++
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f27965caf6a1..99523505dac5 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -475,7 +475,7 @@ static int __arm_lpae_map(struct arm_lpae_io_pgtable *data, unsigned long iova,
 		cptep = iopte_deref(pte, data);
 	} else if (pte) {
 		/* We require an unmap first */
-		WARN_ON(!selftest_running);
+		WARN_ON(!selftest_running && !(cfg->quirks & IO_PGTABLE_QUIRK_NO_WARN_ON));
 		return -EEXIST;
 	}
 
@@ -649,8 +649,10 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
 	unmap_idx_start = ARM_LPAE_LVL_IDX(iova, lvl, data);
 	ptep += unmap_idx_start;
 	pte = READ_ONCE(*ptep);
-	if (WARN_ON(!pte))
-		return 0;
+	if (!pte) {
+		WARN_ON(!(data->iop.cfg.quirks & IO_PGTABLE_QUIRK_NO_WARN_ON));
+		return -ENOENT;
+	}
 
 	/* If the size matches this level, we're in the right place */
 	if (size == ARM_LPAE_BLOCK_SIZE(lvl, data)) {
@@ -660,8 +662,10 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
 		/* Find and handle non-leaf entries */
 		for (i = 0; i < num_entries; i++) {
 			pte = READ_ONCE(ptep[i]);
-			if (WARN_ON(!pte))
+			if (!pte) {
+				WARN_ON(!(data->iop.cfg.quirks & IO_PGTABLE_QUIRK_NO_WARN_ON));
 				break;
+			}
 
 			if (!iopte_leaf(pte, lvl, iop->fmt)) {
 				__arm_lpae_clear_pte(&ptep[i], &iop->cfg, 1);
@@ -976,7 +980,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
 	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
 			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
 			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA |
-			    IO_PGTABLE_QUIRK_ARM_HD))
+			    IO_PGTABLE_QUIRK_ARM_HD |
+			    IO_PGTABLE_QUIRK_NO_WARN_ON))
 		return NULL;
 
 	data = arm_lpae_alloc_pgtable(cfg);
@@ -1079,7 +1084,8 @@ arm_64_lpae_alloc_pgtable_s2(struct io_pgtable_cfg *cfg, void *cookie)
 	struct arm_lpae_io_pgtable *data;
 	typeof(&cfg->arm_lpae_s2_cfg.vtcr) vtcr = &cfg->arm_lpae_s2_cfg.vtcr;
 
-	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_S2FWB))
+	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_S2FWB |
+			    IO_PGTABLE_QUIRK_NO_WARN_ON))
 		return NULL;
 
 	data = arm_lpae_alloc_pgtable(cfg);
diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index bba2a51c87d2..639b8f4fb87d 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -88,6 +88,13 @@ struct io_pgtable_cfg {
 	 *
 	 * IO_PGTABLE_QUIRK_ARM_HD: Enables dirty tracking in stage 1 pagetable.
 	 * IO_PGTABLE_QUIRK_ARM_S2FWB: Use the FWB format for the MemAttrs bits
+	 *
+	 * IO_PGTABLE_QUIRK_NO_WARN_ON: Do not WARN_ON() on conflicting
+	 *	mappings, but silently return -EEXISTS.  Normally an attempt
+	 *	to map over an existing mapping would indicate some sort of
+	 *	kernel bug, which would justify the WARN_ON().  But for GPU
+	 *	drivers, this could be under control of userspace.  Which
+	 *	deserves an error return, but not to spam dmesg.
 	 */
 	#define IO_PGTABLE_QUIRK_ARM_NS			BIT(0)
 	#define IO_PGTABLE_QUIRK_NO_PERMS		BIT(1)
@@ -97,6 +104,7 @@ struct io_pgtable_cfg {
 	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA		BIT(6)
 	#define IO_PGTABLE_QUIRK_ARM_HD			BIT(7)
 	#define IO_PGTABLE_QUIRK_ARM_S2FWB		BIT(8)
+	#define IO_PGTABLE_QUIRK_NO_WARN_ON		BIT(9)
 	unsigned long			quirks;
 	unsigned long			pgsize_bitmap;
 	unsigned int			ias;
-- 
2.49.0