[PATCH v8 0/4] io-pgtable-arm + drm/msm: Extend iova fault debugging

[PATCH v8 0/4] io-pgtable-arm + drm/msm: Extend iova fault debugging

[Rob Clark]

From: Rob Clark <robdclark@chromium.org>

This series extends io-pgtable-arm with a method to retrieve the page
table entries traversed in the process of address translation, and then
beefs up drm/msm gpu devcore dump to include this (and additional info)
in the devcore dump.

This is a respin of https://patchwork.freedesktop.org/series/94968/
(minus a patch that was already merged)

v2: Fix an armv7/32b build error in the last patch
v3: Incorperate Will Deacon's suggestion to make the interface
    callback based.
v4: Actually wire up the callback
v5: Drop the callback approach
v6: Make walk-data struct pgtable specific and rename
    io_pgtable_walk_data to arm_lpae_io_pgtable_walk_data
v7: Re-use the pgtable walker added for arm_lpae_read_and_clear_dirty()
v8: Pass pte pointer to callback so it can modify the actual pte

Rob Clark (4):
  iommu/io-pgtable-arm: Make pgtable walker more generic
  iommu/io-pgtable-arm: Re-use the pgtable walk for iova_to_phys
  iommu/io-pgtable-arm: Add way to debug pgtable walk
  drm/msm: Extend gpu devcore dumps with pgtbl info

 drivers/gpu/drm/msm/adreno/adreno_gpu.c |  10 ++
 drivers/gpu/drm/msm/msm_gpu.c           |   9 ++
 drivers/gpu/drm/msm/msm_gpu.h           |   8 ++
 drivers/gpu/drm/msm/msm_iommu.c         |  22 ++++
 drivers/gpu/drm/msm/msm_mmu.h           |   3 +-
 drivers/iommu/io-pgtable-arm.c          | 147 +++++++++++++++---------
 include/linux/io-pgtable.h              |  15 +++
 7 files changed, 158 insertions(+), 56 deletions(-)

-- 
2.46.0

[PATCH v8 1/4] iommu/io-pgtable-arm: Make pgtable walker more generic

[Rob Clark]

From: Rob Clark <robdclark@chromium.org>

We can re-use this basic pgtable walk logic in a few places.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/iommu/io-pgtable-arm.c | 59 +++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 23 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f5d9fd1f45bf..0132f1eff688 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -747,33 +747,31 @@ static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
 }
 
 struct io_pgtable_walk_data {
-	struct iommu_dirty_bitmap	*dirty;
+	void				*data;
+	int (*visit)(struct io_pgtable_walk_data *walk_data, int lvl,
+		     arm_lpae_iopte *ptep, size_t size);
 	unsigned long			flags;
 	u64				addr;
 	const u64			end;
 };
 
-static int __arm_lpae_iopte_walk_dirty(struct arm_lpae_io_pgtable *data,
-				       struct io_pgtable_walk_data *walk_data,
-				       arm_lpae_iopte *ptep,
-				       int lvl);
+static int __arm_lpae_iopte_walk(struct arm_lpae_io_pgtable *data,
+				 struct io_pgtable_walk_data *walk_data,
+				 arm_lpae_iopte *ptep,
+				 int lvl);
 
-static int io_pgtable_visit_dirty(struct arm_lpae_io_pgtable *data,
-				  struct io_pgtable_walk_data *walk_data,
-				  arm_lpae_iopte *ptep, int lvl)
+static int io_pgtable_visit(struct arm_lpae_io_pgtable *data,
+			    struct io_pgtable_walk_data *walk_data,
+			    arm_lpae_iopte *ptep, int lvl)
 {
 	struct io_pgtable *iop = &data->iop;
 	arm_lpae_iopte pte = READ_ONCE(*ptep);
 
 	if (iopte_leaf(pte, lvl, iop->fmt)) {
 		size_t size = ARM_LPAE_BLOCK_SIZE(lvl, data);
-
-		if (iopte_writeable_dirty(pte)) {
-			iommu_dirty_bitmap_record(walk_data->dirty,
-						  walk_data->addr, size);
-			if (!(walk_data->flags & IOMMU_DIRTY_NO_CLEAR))
-				iopte_set_writeable_clean(ptep);
-		}
+		int ret = walk_data->visit(walk_data, lvl, ptep, size);
+		if (ret)
+			return ret;
 		walk_data->addr += size;
 		return 0;
 	}
@@ -782,13 +780,13 @@ static int io_pgtable_visit_dirty(struct arm_lpae_io_pgtable *data,
 		return -EINVAL;
 
 	ptep = iopte_deref(pte, data);
-	return __arm_lpae_iopte_walk_dirty(data, walk_data, ptep, lvl + 1);
+	return __arm_lpae_iopte_walk(data, walk_data, ptep, lvl + 1);
 }
 
-static int __arm_lpae_iopte_walk_dirty(struct arm_lpae_io_pgtable *data,
-				       struct io_pgtable_walk_data *walk_data,
-				       arm_lpae_iopte *ptep,
-				       int lvl)
+static int __arm_lpae_iopte_walk(struct arm_lpae_io_pgtable *data,
+				 struct io_pgtable_walk_data *walk_data,
+				 arm_lpae_iopte *ptep,
+				 int lvl)
 {
 	u32 idx;
 	int max_entries, ret;
@@ -803,7 +801,7 @@ static int __arm_lpae_iopte_walk_dirty(struct arm_lpae_io_pgtable *data,
 
 	for (idx = ARM_LPAE_LVL_IDX(walk_data->addr, lvl, data);
 	     (idx < max_entries) && (walk_data->addr < walk_data->end); ++idx) {
-		ret = io_pgtable_visit_dirty(data, walk_data, ptep + idx, lvl);
+		ret = io_pgtable_visit(data, walk_data, ptep + idx, lvl);
 		if (ret)
 			return ret;
 	}
@@ -811,6 +809,20 @@ static int __arm_lpae_iopte_walk_dirty(struct arm_lpae_io_pgtable *data,
 	return 0;
 }
 
+static int visit_dirty(struct io_pgtable_walk_data *walk_data, int lvl,
+		       arm_lpae_iopte *ptep, size_t size)
+{
+	struct iommu_dirty_bitmap *dirty = walk_data->data;
+
+	if (iopte_writeable_dirty(*ptep)) {
+		iommu_dirty_bitmap_record(dirty, walk_data->addr, size);
+		if (!(walk_data->flags & IOMMU_DIRTY_NO_CLEAR))
+			iopte_set_writeable_clean(ptep);
+	}
+
+	return 0;
+}
+
 static int arm_lpae_read_and_clear_dirty(struct io_pgtable_ops *ops,
 					 unsigned long iova, size_t size,
 					 unsigned long flags,
@@ -819,7 +831,8 @@ static int arm_lpae_read_and_clear_dirty(struct io_pgtable_ops *ops,
 	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
 	struct io_pgtable_cfg *cfg = &data->iop.cfg;
 	struct io_pgtable_walk_data walk_data = {
-		.dirty = dirty,
+		.data = dirty,
+		.visit = visit_dirty,
 		.flags = flags,
 		.addr = iova,
 		.end = iova + size,
@@ -834,7 +847,7 @@ static int arm_lpae_read_and_clear_dirty(struct io_pgtable_ops *ops,
 	if (data->iop.fmt != ARM_64_LPAE_S1)
 		return -EINVAL;
 
-	return __arm_lpae_iopte_walk_dirty(data, &walk_data, ptep, lvl);
+	return __arm_lpae_iopte_walk(data, &walk_data, ptep, lvl);
 }
 
 static void arm_lpae_restrict_pgsizes(struct io_pgtable_cfg *cfg)
-- 
2.46.0

[PATCH v8 2/4] iommu/io-pgtable-arm: Re-use the pgtable walk for iova_to_phys

[Rob Clark]

From: Rob Clark <robdclark@chromium.org>

Re-use the generic pgtable walk path.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/iommu/io-pgtable-arm.c | 73 +++++++++++++++++-----------------
 1 file changed, 36 insertions(+), 37 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 0132f1eff688..f50ebea85dd8 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -710,42 +710,6 @@ static size_t arm_lpae_unmap_pages(struct io_pgtable_ops *ops, unsigned long iov
 				data->start_level, ptep);
 }
 
-static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
-					 unsigned long iova)
-{
-	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
-	arm_lpae_iopte pte, *ptep = data->pgd;
-	int lvl = data->start_level;
-
-	do {
-		/* Valid IOPTE pointer? */
-		if (!ptep)
-			return 0;
-
-		/* Grab the IOPTE we're interested in */
-		ptep += ARM_LPAE_LVL_IDX(iova, lvl, data);
-		pte = READ_ONCE(*ptep);
-
-		/* Valid entry? */
-		if (!pte)
-			return 0;
-
-		/* Leaf entry? */
-		if (iopte_leaf(pte, lvl, data->iop.fmt))
-			goto found_translation;
-
-		/* Take it to the next level */
-		ptep = iopte_deref(pte, data);
-	} while (++lvl < ARM_LPAE_MAX_LEVELS);
-
-	/* Ran out of page tables to walk */
-	return 0;
-
-found_translation:
-	iova &= (ARM_LPAE_BLOCK_SIZE(lvl, data) - 1);
-	return iopte_to_paddr(pte, data) | iova;
-}
-
 struct io_pgtable_walk_data {
 	void				*data;
 	int (*visit)(struct io_pgtable_walk_data *walk_data, int lvl,
@@ -760,6 +724,41 @@ static int __arm_lpae_iopte_walk(struct arm_lpae_io_pgtable *data,
 				 arm_lpae_iopte *ptep,
 				 int lvl);
 
+struct iova_to_phys_data {
+	arm_lpae_iopte pte;
+	int lvl;
+};
+
+static int visit_iova_to_phys(struct io_pgtable_walk_data *walk_data, int lvl,
+			      arm_lpae_iopte *ptep, size_t size)
+{
+	struct iova_to_phys_data *data = walk_data->data;
+	data->pte = *ptep;
+	data->lvl = lvl;
+	return 0;
+}
+
+static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
+					 unsigned long iova)
+{
+	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
+	struct iova_to_phys_data d;
+	struct io_pgtable_walk_data walk_data = {
+		.data = &d,
+		.visit = visit_iova_to_phys,
+		.addr = iova,
+		.end = iova + 1,
+	};
+	int ret;
+
+	ret = __arm_lpae_iopte_walk(data, &walk_data, data->pgd, data->start_level);
+	if (ret)
+		return 0;
+
+	iova &= (ARM_LPAE_BLOCK_SIZE(d.lvl, data) - 1);
+	return iopte_to_paddr(d.pte, data) | iova;
+}
+
 static int io_pgtable_visit(struct arm_lpae_io_pgtable *data,
 			    struct io_pgtable_walk_data *walk_data,
 			    arm_lpae_iopte *ptep, int lvl)
@@ -776,7 +775,7 @@ static int io_pgtable_visit(struct arm_lpae_io_pgtable *data,
 		return 0;
 	}
 
-	if (WARN_ON(!iopte_table(pte, lvl)))
+	if (WARN_ON(!iopte_table(pte, lvl) && !selftest_running))
 		return -EINVAL;
 
 	ptep = iopte_deref(pte, data);
-- 
2.46.0

[PATCH v8 3/4] iommu/io-pgtable-arm: Add way to debug pgtable walk

[Rob Clark]

From: Rob Clark <robdclark@chromium.org>

Add an io-pgtable method to walk the pgtable returning the raw PTEs that
would be traversed for a given iova access.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/iommu/io-pgtable-arm.c | 25 +++++++++++++++++++++++++
 include/linux/io-pgtable.h     | 15 +++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f50ebea85dd8..2f57a50afe2c 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -759,6 +759,30 @@ static phys_addr_t arm_lpae_iova_to_phys(struct io_pgtable_ops *ops,
 	return iopte_to_paddr(d.pte, data) | iova;
 }
 
+static int visit_pgtable_walk(struct io_pgtable_walk_data *walk_data, int lvl,
+			      arm_lpae_iopte *ptep, size_t size)
+{
+	struct arm_lpae_io_pgtable_walk_data *data = walk_data->data;
+	data->ptes[data->level++] = *ptep;
+	return 0;
+}
+
+static int arm_lpae_pgtable_walk(struct io_pgtable_ops *ops, unsigned long iova,
+				 void *wd)
+{
+	struct arm_lpae_io_pgtable *data = io_pgtable_ops_to_data(ops);
+	struct io_pgtable_walk_data walk_data = {
+		.data = wd,
+		.visit = visit_pgtable_walk,
+		.addr = iova,
+		.end = iova + 1,
+	};
+
+	((struct arm_lpae_io_pgtable_walk_data *)wd)->level = 0;
+
+	return __arm_lpae_iopte_walk(data, &walk_data, data->pgd, data->start_level);
+}
+
 static int io_pgtable_visit(struct arm_lpae_io_pgtable *data,
 			    struct io_pgtable_walk_data *walk_data,
 			    arm_lpae_iopte *ptep, int lvl)
@@ -928,6 +952,7 @@ arm_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg)
 		.unmap_pages	= arm_lpae_unmap_pages,
 		.iova_to_phys	= arm_lpae_iova_to_phys,
 		.read_and_clear_dirty = arm_lpae_read_and_clear_dirty,
+		.pgtable_walk	= arm_lpae_pgtable_walk,
 	};
 
 	return data;
diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index f9a81761bfce..76eabd890e6a 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -174,12 +174,26 @@ struct io_pgtable_cfg {
 	};
 };
 
+/**
+ * struct arm_lpae_io_pgtable_walk_data - information from a pgtable walk
+ *
+ * @ptes:     The recorded PTE values from the walk
+ * @level:    The level of the last PTE
+ *
+ * @level also specifies the last valid index in @ptes
+ */
+struct arm_lpae_io_pgtable_walk_data {
+	u64 ptes[4];
+	int level;
+};
+
 /**
  * struct io_pgtable_ops - Page table manipulation API for IOMMU drivers.
  *
  * @map_pages:    Map a physically contiguous range of pages of the same size.
  * @unmap_pages:  Unmap a range of virtually contiguous pages of the same size.
  * @iova_to_phys: Translate iova to physical address.
+ * @pgtable_walk: (optional) Perform a page table walk for a given iova.
  *
  * These functions map directly onto the iommu_ops member functions with
  * the same names.
@@ -193,6 +207,7 @@ struct io_pgtable_ops {
 			      struct iommu_iotlb_gather *gather);
 	phys_addr_t (*iova_to_phys)(struct io_pgtable_ops *ops,
 				    unsigned long iova);
+	int (*pgtable_walk)(struct io_pgtable_ops *ops, unsigned long iova, void *wd);
 	int (*read_and_clear_dirty)(struct io_pgtable_ops *ops,
 				    unsigned long iova, size_t size,
 				    unsigned long flags,
-- 
2.46.0

[PATCH v8 4/4] drm/msm: Extend gpu devcore dumps with pgtbl info

[Rob Clark]

From: Rob Clark <robdclark@chromium.org>

In the case of iova fault triggered devcore dumps, include additional
debug information based on what we think is the current page tables,
including the TTBR0 value (which should match what we have in
adreno_smmu_fault_info unless things have gone horribly wrong), and
the pagetable entries traversed in the process of resolving the
faulting iova.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/gpu/drm/msm/adreno/adreno_gpu.c | 10 ++++++++++
 drivers/gpu/drm/msm/msm_gpu.c           |  9 +++++++++
 drivers/gpu/drm/msm/msm_gpu.h           |  8 ++++++++
 drivers/gpu/drm/msm/msm_iommu.c         | 22 ++++++++++++++++++++++
 drivers/gpu/drm/msm/msm_mmu.h           |  3 ++-
 5 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
index 1c6626747b98..3848b5a64351 100644
--- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
@@ -864,6 +864,16 @@ void adreno_show(struct msm_gpu *gpu, struct msm_gpu_state *state,
 		drm_printf(p, "  - dir=%s\n", info->flags & IOMMU_FAULT_WRITE ? "WRITE" : "READ");
 		drm_printf(p, "  - type=%s\n", info->type);
 		drm_printf(p, "  - source=%s\n", info->block);
+
+		/* Information extracted from what we think are the current
+		 * pgtables.  Hopefully the TTBR0 matches what we've extracted
+		 * from the SMMU registers in smmu_info!
+		 */
+		drm_puts(p, "pgtable-fault-info:\n");
+		drm_printf(p, "  - ttbr0: %.16llx\n", (u64)info->pgtbl_ttbr0);
+		drm_printf(p, "  - asid: %d\n", info->asid);
+		drm_printf(p, "  - ptes: %.16llx %.16llx %.16llx %.16llx\n",
+			   info->ptes[0], info->ptes[1], info->ptes[2], info->ptes[3]);
 	}
 
 	drm_printf(p, "rbbm-status: 0x%08x\n", state->rbbm_status);
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index 3666b42b4ecd..bf2f8b2a7ccc 100644
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -281,6 +281,15 @@ static void msm_gpu_crashstate_capture(struct msm_gpu *gpu,
 	if (submit) {
 		int i;
 
+		if (state->fault_info.ttbr0) {
+			struct msm_gpu_fault_info *info = &state->fault_info;
+			struct msm_mmu *mmu = submit->aspace->mmu;
+
+			msm_iommu_pagetable_params(mmu, &info->pgtbl_ttbr0,
+						   &info->asid);
+			msm_iommu_pagetable_walk(mmu, info->iova, info->ptes);
+		}
+
 		state->bos = kcalloc(submit->nr_bos,
 			sizeof(struct msm_gpu_state_bo), GFP_KERNEL);
 
diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
index 1f02bb9956be..82e838ba8c80 100644
--- a/drivers/gpu/drm/msm/msm_gpu.h
+++ b/drivers/gpu/drm/msm/msm_gpu.h
@@ -101,6 +101,14 @@ struct msm_gpu_fault_info {
 	int flags;
 	const char *type;
 	const char *block;
+
+	/* Information about what we think/expect is the current SMMU state,
+	 * for example expected_ttbr0 should match smmu_info.ttbr0 which
+	 * was read back from SMMU registers.
+	 */
+	phys_addr_t pgtbl_ttbr0;
+	u64 ptes[4];
+	int asid;
 };
 
 /**
diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
index 2a94e82316f9..3e692818ba1f 100644
--- a/drivers/gpu/drm/msm/msm_iommu.c
+++ b/drivers/gpu/drm/msm/msm_iommu.c
@@ -195,6 +195,28 @@ struct iommu_domain_geometry *msm_iommu_get_geometry(struct msm_mmu *mmu)
 	return &iommu->domain->geometry;
 }
 
+int
+msm_iommu_pagetable_walk(struct msm_mmu *mmu, unsigned long iova, uint64_t ptes[4])
+{
+	struct msm_iommu_pagetable *pagetable;
+	struct arm_lpae_io_pgtable_walk_data wd = {};
+
+	if (mmu->type != MSM_MMU_IOMMU_PAGETABLE)
+		return -EINVAL;
+
+	pagetable = to_pagetable(mmu);
+
+	if (!pagetable->pgtbl_ops->pgtable_walk)
+		return -EINVAL;
+
+	pagetable->pgtbl_ops->pgtable_walk(pagetable->pgtbl_ops, iova, &wd);
+
+	for (int i = 0; i < ARRAY_SIZE(wd.ptes); i++)
+		ptes[i] = wd.ptes[i];
+
+	return 0;
+}
+
 static const struct msm_mmu_funcs pagetable_funcs = {
 		.map = msm_iommu_pagetable_map,
 		.unmap = msm_iommu_pagetable_unmap,
diff --git a/drivers/gpu/drm/msm/msm_mmu.h b/drivers/gpu/drm/msm/msm_mmu.h
index 88af4f490881..96e509bd96a6 100644
--- a/drivers/gpu/drm/msm/msm_mmu.h
+++ b/drivers/gpu/drm/msm/msm_mmu.h
@@ -53,7 +53,8 @@ static inline void msm_mmu_set_fault_handler(struct msm_mmu *mmu, void *arg,
 struct msm_mmu *msm_iommu_pagetable_create(struct msm_mmu *parent);
 
 int msm_iommu_pagetable_params(struct msm_mmu *mmu, phys_addr_t *ttbr,
-		int *asid);
+			       int *asid);
+int msm_iommu_pagetable_walk(struct msm_mmu *mmu, unsigned long iova, uint64_t ptes[4]);
 struct iommu_domain_geometry *msm_iommu_get_geometry(struct msm_mmu *mmu);
 
 #endif /* __MSM_MMU_H__ */
-- 
2.46.0

Re: [PATCH v8 2/4] iommu/io-pgtable-arm: Re-use the pgtable walk for iova_to_phys

[Will Deacon]

On Mon, Aug 26, 2024 at 10:15:39AM -0700, Rob Clark wrote:
> @@ -776,7 +775,7 @@ static int io_pgtable_visit(struct arm_lpae_io_pgtable *data,
>  		return 0;
>  	}
>  
> -	if (WARN_ON(!iopte_table(pte, lvl)))
> +	if (WARN_ON(!iopte_table(pte, lvl) && !selftest_running))
>  		return -EINVAL;
>  
>  	ptep = iopte_deref(pte, data);

I still don't grok this hunk. If the selftest is running, we want to
return -EINVAL here rather than dereference something that isn't a
table, right?

Suppressing the warning is one thing, but this seems to do more than
that.

Will

Re: [PATCH v8 2/4] iommu/io-pgtable-arm: Re-use the pgtable walk for iova_to_phys

[Rob Clark]

On Tue, Aug 27, 2024 at 5:02 AM Will Deacon <will@kernel.org> wrote:
>
> On Mon, Aug 26, 2024 at 10:15:39AM -0700, Rob Clark wrote:
> > @@ -776,7 +775,7 @@ static int io_pgtable_visit(struct arm_lpae_io_pgtable *data,
> >               return 0;
> >       }
> >
> > -     if (WARN_ON(!iopte_table(pte, lvl)))
> > +     if (WARN_ON(!iopte_table(pte, lvl) && !selftest_running))
> >               return -EINVAL;
> >
> >       ptep = iopte_deref(pte, data);
>
> I still don't grok this hunk. If the selftest is running, we want to
> return -EINVAL here rather than dereference something that isn't a
> table, right?
>
> Suppressing the warning is one thing, but this seems to do more than
> that.

oh, that should be

   if (!iopte_table(...)) {
      WARN_ON(!selftest_running);
      return -EINVAL;
   }

I did boot with selftests enabled, and it didn't _seem_ to complain
about anything, so I overlooked that

BR,
-R

>
> Will