[PATCH 0/3] iommu/io-pgtable-arm: iommu-pages and cleanup

[PATCH 0/3] iommu/io-pgtable-arm: iommu-pages and cleanup

[Mostafa Saleh]

This is a small cleanup coming from the pKVM SMMUv3 support [1].
However, they are not pKVM specific and useful in general.

The first patch is to fix a theoretical issues with alloc/free size.
The second patch is the main one to convert the code to iommu-pages.
The third patch is a cleanup to use address conversion consistently.

[1] https://lore.kernel.org/linux-iommu/20260501111928.259252-1-smostafa@google.com/

Mostafa Saleh (3):
  iommu/io-pgtable-arm: Use consistent sizes for page allocation and
    freeing
  iommu/io-pgtable-arm: Rework to use the iommu-pages API
  iommu/io-pgtable-arm: Use address conversion consistently

 drivers/iommu/io-pgtable-arm.c | 88 +++++++++++++++++++++++-----------
 1 file changed, 61 insertions(+), 27 deletions(-)

-- 
2.54.0.563.g4f69b47b94-goog

[PATCH 1/3] iommu/io-pgtable-arm: Use consistent sizes for page allocation and freeing

[Mostafa Saleh]

At the moment we use alloc_size to allocate memory but then there
is a logical error where we just size in the error and free path,
which might be smaller.
Also we size to do DMA-API operations, which is OK, but confusing.

Instead of this error-prone handling, just set size to alloc_size
and use it everywhere.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
 drivers/iommu/io-pgtable-arm.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 0208e5897c29..0cbe545c491d 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -253,7 +253,6 @@ static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
 				    void *cookie)
 {
 	struct device *dev = cfg->iommu_dev;
-	size_t alloc_size;
 	dma_addr_t dma;
 	void *pages;
 
@@ -261,12 +260,11 @@ static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
 	 * For very small starting-level translation tables the HW requires a
 	 * minimum alignment of at least 64 to cover all cases.
 	 */
-	alloc_size = max(size, 64);
+	size = max(size, 64);
 	if (cfg->alloc)
-		pages = cfg->alloc(cookie, alloc_size, gfp);
+		pages = cfg->alloc(cookie, size, gfp);
 	else
-		pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp,
-						  alloc_size);
+		pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp, size);
 
 	if (!pages)
 		return NULL;
@@ -303,6 +301,9 @@ static void __arm_lpae_free_pages(void *pages, size_t size,
 				  struct io_pgtable_cfg *cfg,
 				  void *cookie)
 {
+	/* See __arm_lpae_alloc_pages(). */
+	size = max(size, 64);
+
 	if (!cfg->coherent_walk)
 		dma_unmap_single(cfg->iommu_dev, __arm_lpae_dma_addr(pages),
 				 size, DMA_TO_DEVICE);
-- 
2.54.0.563.g4f69b47b94-goog

Re: [PATCH 1/3] iommu/io-pgtable-arm: Use consistent sizes for page allocation and freeing

[Jason Gunthorpe]

On Wed, May 13, 2026 at 09:52:01PM +0000, Mostafa Saleh wrote:
> At the moment we use alloc_size to allocate memory but then there
> is a logical error where we just size in the error and free path,
> which might be smaller.
> Also we size to do DMA-API operations, which is OK, but confusing.
> 
> Instead of this error-prone handling, just set size to alloc_size
> and use it everywhere.
> 
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
>  drivers/iommu/io-pgtable-arm.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

This is similar to how iommupt works, pt_top_memsize_lg2() rounds up
the top table size to the alignment minimum and we just dma map
flush/etc the larger size everwhere.

Jason

[PATCH 2/3] iommu/io-pgtable-arm: Rework to use the iommu-pages API

[Mostafa Saleh]

Update the io-pgtable-arm allocator to use the iommu-pages API.

Replace the DMA API usage from __arm_lpae_alloc_pages() with
iommu_pages_start_incoherent() and from __arm_lpae_free_pages() with
iommu_pages_free_incoherent().

Since the iommu-pages API relies on metadata stored in the struct page
during iommu_alloc_pages_node_sz(), it cannot be used safely with memory
allocated via the custom cfg->alloc (which may not be backed by pages).
So, isolate that logic and keep it as it.

Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
 drivers/iommu/io-pgtable-arm.c | 79 ++++++++++++++++++++++++----------
 1 file changed, 56 insertions(+), 23 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 0cbe545c491d..86b23aa04324 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -248,24 +248,15 @@ static dma_addr_t __arm_lpae_dma_addr(void *pages)
 	return (dma_addr_t)virt_to_phys(pages);
 }
 
-static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
-				    struct io_pgtable_cfg *cfg,
-				    void *cookie)
+static void *__arm_lpae_cfg_alloc(size_t size, gfp_t gfp,
+				  struct io_pgtable_cfg *cfg,
+				  void *cookie)
 {
 	struct device *dev = cfg->iommu_dev;
 	dma_addr_t dma;
 	void *pages;
 
-	/*
-	 * For very small starting-level translation tables the HW requires a
-	 * minimum alignment of at least 64 to cover all cases.
-	 */
-	size = max(size, 64);
-	if (cfg->alloc)
-		pages = cfg->alloc(cookie, size, gfp);
-	else
-		pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp, size);
-
+	pages = cfg->alloc(cookie, size, gfp);
 	if (!pages)
 		return NULL;
 
@@ -289,14 +280,55 @@ static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
 	dma_unmap_single(dev, dma, size, DMA_TO_DEVICE);
 
 out_free:
-	if (cfg->free)
-		cfg->free(cookie, pages, size);
-	else
-		iommu_free_pages(pages);
-
+	cfg->free(cookie, pages, size);
 	return NULL;
 }
 
+static void __arm_lpae_cfg_free(void *pages, size_t size,
+				struct io_pgtable_cfg *cfg,
+				void *cookie)
+{
+	if (!cfg->coherent_walk)
+		dma_unmap_single(cfg->iommu_dev, __arm_lpae_dma_addr(pages),
+				 size, DMA_TO_DEVICE);
+
+	cfg->free(cookie, pages, size);
+}
+
+static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
+				    struct io_pgtable_cfg *cfg,
+				    void *cookie)
+{
+	struct device *dev = cfg->iommu_dev;
+	void *pages;
+
+	/*
+	 * For very small starting-level translation tables the HW requires a
+	 * minimum alignment of at least 64 to cover all cases.
+	 */
+	size = max(size, 64);
+
+	if (cfg->alloc)
+		return __arm_lpae_cfg_alloc(size, gfp, cfg, cookie);
+
+	pages = iommu_alloc_pages_node_sz(dev_to_node(dev), gfp, size);
+	if (!pages)
+		return NULL;
+
+	if (!cfg->coherent_walk) {
+		int ret = iommu_pages_start_incoherent(pages, dev);
+
+		if (ret) {
+			if (ret == -EOPNOTSUPP)
+				dev_err(dev, "Cannot accommodate DMA translation for IOMMU page tables\n");
+			iommu_free_pages(pages);
+			return NULL;
+		}
+	}
+
+	return pages;
+}
+
 static void __arm_lpae_free_pages(void *pages, size_t size,
 				  struct io_pgtable_cfg *cfg,
 				  void *cookie)
@@ -304,12 +336,13 @@ static void __arm_lpae_free_pages(void *pages, size_t size,
 	/* See __arm_lpae_alloc_pages(). */
 	size = max(size, 64);
 
-	if (!cfg->coherent_walk)
-		dma_unmap_single(cfg->iommu_dev, __arm_lpae_dma_addr(pages),
-				 size, DMA_TO_DEVICE);
+	if (cfg->free) {
+		__arm_lpae_cfg_free(pages, size, cfg, cookie);
+		return;
+	}
 
-	if (cfg->free)
-		cfg->free(cookie, pages, size);
+	if (!cfg->coherent_walk)
+		iommu_pages_free_incoherent(pages, cfg->iommu_dev);
 	else
 		iommu_free_pages(pages);
 }
-- 
2.54.0.563.g4f69b47b94-goog

Re: [PATCH 2/3] iommu/io-pgtable-arm: Rework to use the iommu-pages API

[Jason Gunthorpe]

On Wed, May 13, 2026 at 09:52:02PM +0000, Mostafa Saleh wrote:
> Update the io-pgtable-arm allocator to use the iommu-pages API.
> 
> Replace the DMA API usage from __arm_lpae_alloc_pages() with
> iommu_pages_start_incoherent() and from __arm_lpae_free_pages() with
> iommu_pages_free_incoherent().
> 
> Since the iommu-pages API relies on metadata stored in the struct page
> during iommu_alloc_pages_node_sz(), it cannot be used safely with memory
> allocated via the custom cfg->alloc (which may not be backed by pages).
> So, isolate that logic and keep it as it.
> 
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
>  drivers/iommu/io-pgtable-arm.c | 79 ++++++++++++++++++++++++----------
>  1 file changed, 56 insertions(+), 23 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

I feel the setup for incoherent walk for panthor is kind of sketchy,
if you select incoherent walk and pass in a random GPU driver struct
device there are alot of assumptions suddenly to know the dma API is
doing the right thing..

Jason

[PATCH 3/3] iommu/io-pgtable-arm: Use address conversion consistently

[Mostafa Saleh]

Use consistent address conversions in the driver:
- virt_to_phys(): For all virtual to physical address conversion,
  convert __pa users as we don’t need to rely on it type casting.
- phys_to_virt(): For all physical to virtual address conversion,
  similarly, convert __va users.

That changes nothing at all. However, it will be useful when
compiling this file for the KVM hypervisor as it can cleanly
replace virt_to_phys/phys_to_virt

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
 drivers/iommu/io-pgtable-arm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 86b23aa04324..476c0e25631a 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -143,7 +143,7 @@
 #define ARM_MALI_LPAE_MEMATTR_WRITE_ALLOC 0x8DULL
 
 /* IOPTE accessors */
-#define iopte_deref(pte,d) __va(iopte_to_paddr(pte, d))
+#define iopte_deref(pte, d) phys_to_virt(iopte_to_paddr(pte, d))
 
 #define iopte_type(pte)					\
 	(((pte) >> ARM_LPAE_PTE_TYPE_SHIFT) & ARM_LPAE_PTE_TYPE_MASK)
@@ -429,7 +429,7 @@ static arm_lpae_iopte arm_lpae_install_table(arm_lpae_iopte *table,
 	arm_lpae_iopte old, new;
 	struct io_pgtable_cfg *cfg = &data->iop.cfg;
 
-	new = paddr_to_iopte(__pa(table), data) | ARM_LPAE_PTE_TYPE_TABLE;
+	new = paddr_to_iopte(virt_to_phys(table), data) | ARM_LPAE_PTE_TYPE_TABLE;
 	if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_NS)
 		new |= ARM_LPAE_PTE_NSTABLE;
 
-- 
2.54.0.563.g4f69b47b94-goog

Re: [PATCH 3/3] iommu/io-pgtable-arm: Use address conversion consistently

[Jason Gunthorpe]

On Wed, May 13, 2026 at 09:52:03PM +0000, Mostafa Saleh wrote:
> Use consistent address conversions in the driver:
> - virt_to_phys(): For all virtual to physical address conversion,
>   convert __pa users as we don’t need to rely on it type casting.
> - phys_to_virt(): For all physical to virtual address conversion,
>   similarly, convert __va users.
> 
> That changes nothing at all. However, it will be useful when
> compiling this file for the KVM hypervisor as it can cleanly
> replace virt_to_phys/phys_to_virt
> 
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
>  drivers/iommu/io-pgtable-arm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason

Re: [PATCH 0/3] iommu/io-pgtable-arm: iommu-pages and cleanup

[Jörg Rödel]

On Wed, May 13, 2026 at 09:52:00PM +0000, Mostafa Saleh wrote:
> Mostafa Saleh (3):
>   iommu/io-pgtable-arm: Use consistent sizes for page allocation and
>     freeing
>   iommu/io-pgtable-arm: Rework to use the iommu-pages API
>   iommu/io-pgtable-arm: Use address conversion consistently
> 
>  drivers/iommu/io-pgtable-arm.c | 88 +++++++++++++++++++++++-----------
>  1 file changed, 61 insertions(+), 27 deletions(-)

Applied, thanks.