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[PATCH 5/8] kmsan: convert kmsan_handle_dma to use physical addresses

Leon Romanovsky posted 8 patches 3 months, 2 weeks ago
There is a newer version of this series
[PATCH 5/8] kmsan: convert kmsan_handle_dma to use physical addresses
Posted by Leon Romanovsky 3 months, 2 weeks ago 
From: Leon Romanovsky <leonro@nvidia.com>

Convert the KMSAN DMA handling function from page-based to physical
address-based interface.

The refactoring renames kmsan_handle_dma() parameters from accepting
(struct page *page, size_t offset, size_t size) to (phys_addr_t phys,
size_t size). A PFN_VALID check is added to prevent KMSAN operations
on non-page memory, preventing from non struct page backed address,

As part of this change, support for highmem addresses is implemented
using kmap_local_page() to handle both lowmem and highmem regions
properly. All callers throughout the codebase are updated to use the
new phys_addr_t based interface.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/virtio/virtio_ring.c |  4 ++--
 include/linux/kmsan.h        | 12 +++++++-----
 kernel/dma/mapping.c         |  2 +-
 mm/kmsan/hooks.c             | 36 +++++++++++++++++++++++++++++-------
 tools/virtio/linux/kmsan.h   |  2 +-
 5 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b784aab66867..dab49385e3e8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -378,7 +378,7 @@ static int vring_map_one_sg(const struct vring_virtqueue *vq, struct scatterlist
 		 * is initialized by the hardware. Explicitly check/unpoison it
 		 * depending on the direction.
 		 */
-		kmsan_handle_dma(sg_page(sg), sg->offset, sg->length, direction);
+		kmsan_handle_dma(sg_phys(sg), sg->length, direction);
 		*addr = (dma_addr_t)sg_phys(sg);
 		return 0;
 	}
@@ -3149,7 +3149,7 @@ dma_addr_t virtqueue_dma_map_single_attrs(struct virtqueue *_vq, void *ptr,
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
 	if (!vq->use_dma_api) {
-		kmsan_handle_dma(virt_to_page(ptr), offset_in_page(ptr), size, dir);
+		kmsan_handle_dma(virt_to_phys(ptr), size, dir);
 		return (dma_addr_t)virt_to_phys(ptr);
 	}
 
diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
index 2b1432cc16d5..6f27b9824ef7 100644
--- a/include/linux/kmsan.h
+++ b/include/linux/kmsan.h
@@ -182,8 +182,7 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end);
 
 /**
  * kmsan_handle_dma() - Handle a DMA data transfer.
- * @page:   first page of the buffer.
- * @offset: offset of the buffer within the first page.
+ * @phys:   physical address of the buffer.
  * @size:   buffer size.
  * @dir:    one of possible dma_data_direction values.
  *
@@ -191,8 +190,11 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end);
  * * checks the buffer, if it is copied to device;
  * * initializes the buffer, if it is copied from device;
  * * does both, if this is a DMA_BIDIRECTIONAL transfer.
+ *
+ * The function handles page lookup internally and supports both lowmem
+ * and highmem addresses.
  */
-void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
+void kmsan_handle_dma(phys_addr_t phys, size_t size,
 		      enum dma_data_direction dir);
 
 /**
@@ -372,8 +374,8 @@ static inline void kmsan_iounmap_page_range(unsigned long start,
 {
 }
 
-static inline void kmsan_handle_dma(struct page *page, size_t offset,
-				    size_t size, enum dma_data_direction dir)
+static inline void kmsan_handle_dma(phys_addr_t phys, size_t size,
+				    enum dma_data_direction dir)
 {
 }
 
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 80481a873340..709405d46b2b 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -172,7 +172,7 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
 		addr = iommu_dma_map_phys(dev, phys, size, dir, attrs);
 	else
 		addr = ops->map_page(dev, page, offset, size, dir, attrs);
-	kmsan_handle_dma(page, offset, size, dir);
+	kmsan_handle_dma(phys, size, dir);
 	trace_dma_map_phys(dev, phys, addr, size, dir, attrs);
 	debug_dma_map_phys(dev, phys, size, dir, addr, attrs);
 
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 97de3d6194f0..eab7912a3bf0 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -336,25 +336,48 @@ static void kmsan_handle_dma_page(const void *addr, size_t size,
 }
 
 /* Helper function to handle DMA data transfers. */
-void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
+void kmsan_handle_dma(phys_addr_t phys, size_t size,
 		      enum dma_data_direction dir)
 {
 	u64 page_offset, to_go, addr;
+	struct page *page;
+	void *kaddr;
 
-	if (PageHighMem(page))
+	if (!pfn_valid(PHYS_PFN(phys)))
 		return;
-	addr = (u64)page_address(page) + offset;
+
+	page = phys_to_page(phys);
+	page_offset = offset_in_page(phys);
+
 	/*
 	 * The kernel may occasionally give us adjacent DMA pages not belonging
 	 * to the same allocation. Process them separately to avoid triggering
 	 * internal KMSAN checks.
 	 */
 	while (size > 0) {
-		page_offset = offset_in_page(addr);
 		to_go = min(PAGE_SIZE - page_offset, (u64)size);
+
+		if (PageHighMem(page))
+			/* Handle highmem pages using kmap */
+			kaddr = kmap_local_page(page);
+		else
+			/* Lowmem pages can be accessed directly */
+			kaddr = page_address(page);
+
+		addr = (u64)kaddr + page_offset;
 		kmsan_handle_dma_page((void *)addr, to_go, dir);
-		addr += to_go;
+
+		if (PageHighMem(page))
+			kunmap_local(page);
+
+		phys += to_go;
 		size -= to_go;
+
+		/* Move to next page if needed */
+		if (size > 0) {
+			page = phys_to_page(phys);
+			page_offset = offset_in_page(phys);
+		}
 	}
 }
 EXPORT_SYMBOL_GPL(kmsan_handle_dma);
@@ -366,8 +389,7 @@ void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
 	int i;
 
 	for_each_sg(sg, item, nents, i)
-		kmsan_handle_dma(sg_page(item), item->offset, item->length,
-				 dir);
+		kmsan_handle_dma(sg_phys(item), item->length, dir);
 }
 
 /* Functions from kmsan-checks.h follow. */
diff --git a/tools/virtio/linux/kmsan.h b/tools/virtio/linux/kmsan.h
index 272b5aa285d5..6cd2e3efd03d 100644
--- a/tools/virtio/linux/kmsan.h
+++ b/tools/virtio/linux/kmsan.h
@@ -4,7 +4,7 @@
 
 #include <linux/gfp.h>
 
-inline void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
+inline void kmsan_handle_dma(phys_addr_t phys, size_t size,
 			     enum dma_data_direction dir)
 {
 }
-- 
2.49.0
Re: [PATCH 5/8] kmsan: convert kmsan_handle_dma to use physical addresses
Posted by Alexander Potapenko 3 months, 1 week ago 
On Wed, Jun 25, 2025 at 3:19 PM Leon Romanovsky <leon@kernel.org> wrote:
>
> From: Leon Romanovsky <leonro@nvidia.com>

Hi Leon,

>
> Convert the KMSAN DMA handling function from page-based to physical
> address-based interface.
>
> The refactoring renames kmsan_handle_dma() parameters from accepting
> (struct page *page, size_t offset, size_t size) to (phys_addr_t phys,
> size_t size).

Could you please elaborate a bit why this is needed? Are you fixing
some particular issue?

> A PFN_VALID check is added to prevent KMSAN operations
> on non-page memory, preventing from non struct page backed address,
>
> As part of this change, support for highmem addresses is implemented
> using kmap_local_page() to handle both lowmem and highmem regions
> properly. All callers throughout the codebase are updated to use the
> new phys_addr_t based interface.

KMSAN only works on 64-bit systems, do we actually have highmem on any of these?
Re: [PATCH 5/8] kmsan: convert kmsan_handle_dma to use physical addresses
Posted by Leon Romanovsky 3 months, 1 week ago 
On Thu, Jun 26, 2025 at 07:43:06PM +0200, Alexander Potapenko wrote:
> On Wed, Jun 25, 2025 at 3:19 PM Leon Romanovsky <leon@kernel.org> wrote:
> >
> > From: Leon Romanovsky <leonro@nvidia.com>
> 
> Hi Leon,
> 
> >
> > Convert the KMSAN DMA handling function from page-based to physical
> > address-based interface.
> >
> > The refactoring renames kmsan_handle_dma() parameters from accepting
> > (struct page *page, size_t offset, size_t size) to (phys_addr_t phys,
> > size_t size).
> 
> Could you please elaborate a bit why this is needed? Are you fixing
> some particular issue?

It is soft of the fix and improvement at the same time.
Improvement: 
It allows direct call to kmsan_handle_dma() without need
to convert from phys_addr_t to struct page for newly introduced
dma_map_phys() routine.

Fix:
It prevents us from executing kmsan for addresses that don't have struct page
(for example PCI_P2PDMA_MAP_THRU_HOST_BRIDGE pages), which we are doing
with original code.

dma_map_sg_attrs()
 -> __dma_map_sg_attrs()
  -> dma_direct_map_sg()
   -> PCI_P2PDMA_MAP_THRU_HOST_BRIDGE and nents > 0
    -> kmsan_handle_dma_sg();
     -> kmsan_handle_dma(g_page(item) <---- this is "fake" page.

We are trying to build DMA API that doesn't require struct pages.

> 
> > A PFN_VALID check is added to prevent KMSAN operations
> > on non-page memory, preventing from non struct page backed address,
> >
> > As part of this change, support for highmem addresses is implemented
> > using kmap_local_page() to handle both lowmem and highmem regions
> > properly. All callers throughout the codebase are updated to use the
> > new phys_addr_t based interface.
> 
> KMSAN only works on 64-bit systems, do we actually have highmem on any of these?

I don't know, but the original code had this check:
  344         if (PageHighMem(page)) 
  345                 return;

Thanks
Re: [PATCH 5/8] kmsan: convert kmsan_handle_dma to use physical addresses
Posted by Alexander Potapenko 3 months, 1 week ago 
On Thu, Jun 26, 2025 at 8:45 PM Leon Romanovsky <leon@kernel.org> wrote:
>
> On Thu, Jun 26, 2025 at 07:43:06PM +0200, Alexander Potapenko wrote:
> > On Wed, Jun 25, 2025 at 3:19 PM Leon Romanovsky <leon@kernel.org> wrote:
> > >
> > > From: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Alexander Potapenko <glider@google.com>

> >
> > Hi Leon,
> >
> > >
> > > Convert the KMSAN DMA handling function from page-based to physical
> > > address-based interface.
> > >
> > > The refactoring renames kmsan_handle_dma() parameters from accepting
> > > (struct page *page, size_t offset, size_t size) to (phys_addr_t phys,
> > > size_t size).
> >
> > Could you please elaborate a bit why this is needed? Are you fixing
> > some particular issue?
>
> It is soft of the fix and improvement at the same time.
> Improvement:
> It allows direct call to kmsan_handle_dma() without need
> to convert from phys_addr_t to struct page for newly introduced
> dma_map_phys() routine.
>
> Fix:
> It prevents us from executing kmsan for addresses that don't have struct page
> (for example PCI_P2PDMA_MAP_THRU_HOST_BRIDGE pages), which we are doing
> with original code.
>
> dma_map_sg_attrs()
>  -> __dma_map_sg_attrs()
>   -> dma_direct_map_sg()
>    -> PCI_P2PDMA_MAP_THRU_HOST_BRIDGE and nents > 0
>     -> kmsan_handle_dma_sg();
>      -> kmsan_handle_dma(g_page(item) <---- this is "fake" page.
>
> We are trying to build DMA API that doesn't require struct pages.

Thanks for clarifying that!

> > KMSAN only works on 64-bit systems, do we actually have highmem on any of these?
>
> I don't know, but the original code had this check:
>   344         if (PageHighMem(page))
>   345                 return;
>
> Thanks

Ouch, I overlooked that, sorry!

I spent a while trying to understand where this code originated from,
and found the following discussion:
https://lore.kernel.org/all/20200327170647.GA22758@lst.de/

It's still unclear to me whether we actually need this check, because
with my config it doesn't produce any code.
But I think this shouldn't be blocking your patch, I'd rather make a
follow-up fix.

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