diff mbox series

[1/2] dma-mapping: remove bogus test for pfn_valid from dma_map_resource

Message ID 20210930013039.11260-2-rppt@kernel.org (mailing list archive)
State New, archived
Headers show
Series arm64: retry dropping HAVE_ARCH_PFN_VALID | expand

Commit Message

Mike Rapoport Sept. 30, 2021, 1:30 a.m. UTC 
From: Mike Rapoport <rppt@linux.ibm.com>

dma_map_resource() uses pfn_valid() to ensure the range is not RAM.
However, pfn_valid() only checks for availability of the memory map for a
PFN but it does not ensure that the PFN is actually backed by RAM.

As dma_map_resource() is the only method in DMA mapping APIs that has this
check, simply drop the pfn_valid() test from dma_map_resource().

Link: https://lore.kernel.org/all/20210824173741.GC623@arm.com/
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
 kernel/dma/mapping.c | 4 ----
 1 file changed, 4 deletions(-)

Comments

Christoph Hellwig Sept. 30, 2021, 5:46 a.m. UTC | #1 
On Thu, Sep 30, 2021 at 04:30:38AM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> dma_map_resource() uses pfn_valid() to ensure the range is not RAM.
> However, pfn_valid() only checks for availability of the memory map for a
> PFN but it does not ensure that the PFN is actually backed by RAM.
> 
> As dma_map_resource() is the only method in DMA mapping APIs that has this
> check, simply drop the pfn_valid() test from dma_map_resource().
> 
> Link: https://lore.kernel.org/all/20210824173741.GC623@arm.com/
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>

We'll lose a bit of a sanity check with this, but given the problems it
caused:

Reviewed-by: Christoph Hellwig <hch@lst.de>
David Hildenbrand Sept. 30, 2021, 7:27 a.m. UTC | #2 
On 30.09.21 03:30, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> dma_map_resource() uses pfn_valid() to ensure the range is not RAM.
> However, pfn_valid() only checks for availability of the memory map for a
> PFN but it does not ensure that the PFN is actually backed by RAM.
> 
> As dma_map_resource() is the only method in DMA mapping APIs that has this
> check, simply drop the pfn_valid() test from dma_map_resource().
> 
> Link: https://lore.kernel.org/all/20210824173741.GC623@arm.com/
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>
diff mbox series

Patch

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 06fec5547e7c..dda8d8b84a55 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -296,10 +296,6 @@  dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
 	if (WARN_ON_ONCE(!dev->dma_mask))
 		return DMA_MAPPING_ERROR;
 
-	/* Don't allow RAM to be mapped */
-	if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
-		return DMA_MAPPING_ERROR;
-
 	if (dma_map_direct(dev, ops))
 		addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
 	else if (ops->map_resource)