Re: [PATCH v2] iommu/io-pgtable-arm: Add quirk to quiet WARN_ON()

Signed-off-by: Rob Clark <redacted>
---
Sending v2 stand-alone, since I'm not quite ready to send a new
iteration of the full VM_BIND series.  And with selftest_running
removed, I think this patch stands on it's own.  (And maybe there
is still time to sneak this in for v6.16, removing an iommu dep
for the VM_BIND series in v6.17?)

v2: Drop selftest_running and use IO_PGTABLE_QUIRK_NO_WARN_ON for
     the selftests

  drivers/iommu/io-pgtable-arm.c | 27 ++++++++++++++-------------
  include/linux/io-pgtable.h     |  8 ++++++++
  2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f27965caf6a1..a535d88f8943 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c

@@ -253,8 +253,6 @@ 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);

@@ -373,7 +371,7 @@ 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_ON));
  			return -EEXIST;
  		} else if (iopte_type(ptep[i]) == ARM_LPAE_PTE_TYPE_TABLE) {
  			/*

@@ -475,7 +473,7 @@ 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_ON));
  		return -EEXIST;
  	}
  

@@ -649,8 +647,10 @@ 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 +660,10 @@ 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 +978,8 @@ 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 +1082,8 @@ 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);

@@ -1320,7 +1324,6 @@ 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;						\
  })
  

@@ -1336,8 +1339,6 @@ 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);

@@ -1426,7 +1427,6 @@ static int __init arm_lpae_run_tests(struct io_pgtable_cfg *cfg)
  		free_io_pgtable_ops(ops);
  	}
  
-	selftest_running = false;
  	return 0;
  }
  

@@ -1448,6 +1448,7 @@ static int __init arm_lpae_do_selftests(void)
  		.tlb = &dummy_tlb_ops,
  		.coherent_walk = true,
  		.iommu_dev = &dev,
+		.quirks = IO_PGTABLE_QUIRK_NO_WARN_ON,
  	};
  
  	/* __arm_lpae_alloc_pages() merely needs dev_to_node() to work */

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;