iommu/io-pgtable-arm: Add quirk to quiet WARN_ON()

In situations where mapping/unmapping sequence 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.

Now that there is a quirk, we can also drop the selftest_running
flag, and use the quirk instead for selftests.

Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20250519175348.11924-6-robdclark@gmail.com
[will: Rename quirk to IO_PGTABLE_QUIRK_NO_WARN per Robin's suggestion]
Signed-off-by: Will Deacon <will@kernel.org>

drivers/iommu/io-pgtable-arm.c

@@ -251,8 +251,6 @@ static inline bool arm_lpae_concat_mandatory(struct io_pgtable_cfg *cfg,
 	       (data->start_level == 1) && (oas == 40);
 }
 
-static bool selftest_running = false;
-
 static dma_addr_t __arm_lpae_dma_addr(void *pages)
 {
 	return (dma_addr_t)virt_to_phys(pages);
@@ -371,7 +369,7 @@ static int arm_lpae_init_pte(struct arm_lpae_io_pgtable *data,
 	for (i = 0; i < num_entries; i++)
 		if (iopte_leaf(ptep[i], lvl, data->iop.fmt)) {
 			/* We require an unmap first */
-			WARN_ON(!selftest_running);
+			WARN_ON(!(data->iop.cfg.quirks & IO_PGTABLE_QUIRK_NO_WARN));
 			return -EEXIST;
 		} else if (iopte_type(ptep[i]) == ARM_LPAE_PTE_TYPE_TABLE) {
 			/*
@@ -473,7 +471,7 @@ 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(!(cfg->quirks & IO_PGTABLE_QUIRK_NO_WARN));
 		return -EEXIST;
 	}
 
@@ -641,8 +639,10 @@ 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))
+	if (!pte) {
-		return 0;
+		WARN_ON(!(data->iop.cfg.quirks & IO_PGTABLE_QUIRK_NO_WARN));
+		return -ENOENT;
+	}
 
 	/* If the size matches this level, we're in the right place */
 	if (size == ARM_LPAE_BLOCK_SIZE(lvl, data)) {
@@ -652,8 +652,10 @@ 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));
 				break;
+			}
 
 			if (!iopte_leaf(pte, lvl, iop->fmt)) {
 				__arm_lpae_clear_pte(&ptep[i], &iop->cfg, 1);
@@ -968,7 +970,8 @@ 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))
 		return NULL;
 
 	data = arm_lpae_alloc_pgtable(cfg);
@@ -1069,7 +1072,8 @@ 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))
 		return NULL;
 
 	data = arm_lpae_alloc_pgtable(cfg);
@@ -1310,7 +1314,6 @@ static void __init arm_lpae_dump_ops(struct io_pgtable_ops *ops)
 #define __FAIL(ops, i)	({						\
 		WARN(1, "selftest: test failed for fmt idx %d\n", (i));	\
 		arm_lpae_dump_ops(ops);					\
-		selftest_running = false;				\
 		-EFAULT;						\
 })
 
@@ -1326,8 +1329,6 @@ static int __init arm_lpae_run_tests(struct io_pgtable_cfg *cfg)
 	size_t size, mapped;
 	struct io_pgtable_ops *ops;
 
-	selftest_running = true;
-
 	for (i = 0; i < ARRAY_SIZE(fmts); ++i) {
 		cfg_cookie = cfg;
 		ops = alloc_io_pgtable_ops(fmts[i], cfg, cfg);
@@ -1416,7 +1417,6 @@ static int __init arm_lpae_run_tests(struct io_pgtable_cfg *cfg)
 		free_io_pgtable_ops(ops);
 	}
 
-	selftest_running = false;
 	return 0;
 }
 
@@ -1438,6 +1438,7 @@ static int __init arm_lpae_do_selftests(void)
 		.tlb = &dummy_tlb_ops,
 		.coherent_walk = true,
 		.iommu_dev = &dev,
+		.quirks = IO_PGTABLE_QUIRK_NO_WARN,
 	};
 
 	/* __arm_lpae_alloc_pages() merely needs dev_to_node() to work */

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: 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		BIT(9)
 	unsigned long			quirks;
 	unsigned long			pgsize_bitmap;
 	unsigned int			ias;