On 13/04/18 18:25, Jacopo Mondi wrote:
Postpone calling virt_to_page() translation on memory locations not
guaranteed to be backed by a struct page. Try first to map memory from
device's coherent memory pool, then perform translation if that fails.
On some architectures, specifically SH when configured with SPARSEMEM
memory model, assuming a struct page is always assigned to a memory
address lead to unexpected hangs during the virtual to page address
translation. This patch fixes that specific issue but applies in the
general case too.
Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
Suggested-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
---
It has now been clarified this patch does not resolve the issue, but only
mitigate it on platforms where dma_mmap_from_dev_coherent() succeeds and
delay page_to_pfn() faulty conversion.
A suggested proper solution would be not relying on dma_common_mmap() but
require all platforms to implement an mmap methods known to work, as noted
by Christoph in v1 review.
Note that that "proper solution" should still involve having
dma_common_mmap() since we certainly don't want an explosion of code
duplication. It just means that architectures that do use it should be
defining their dma_map_ops with an explicit ".mmap = dma_common_mmap"
instead of relying on dma_mmap_attrs() calling it by default. Thus the
more architectures this implementation *is* definitely safe for, the
better :)
Robin.
v1 -> v2:
- Save the 'pfn' temp variable performing the page_to_pfn() conversion in the
remap_pfn_range() function call as suggested by Christoph.
---
drivers/base/dma-mapping.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
index 3b11835..d82566d 100644
--- a/drivers/base/dma-mapping.c
+++ b/drivers/base/dma-mapping.c
@@ -226,7 +226,6 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
#ifndef CONFIG_ARCH_NO_COHERENT_DMA_MMAP
unsigned long user_count = vma_pages(vma);
unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
- unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
unsigned long off = vma->vm_pgoff;
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
@@ -234,12 +233,11 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
if (dma_mmap_from_dev_coherent(dev, vma, cpu_addr, size, &ret))
return ret;
- if (off < count && user_count <= (count - off)) {
+ if (off < count && user_count <= (count - off))
ret = remap_pfn_range(vma, vma->vm_start,
- pfn + off,
+ page_to_pfn(virt_to_page(cpu_addr)) + off,
user_count << PAGE_SHIFT,
vma->vm_page_prot);
- }
#endif /* !CONFIG_ARCH_NO_COHERENT_DMA_MMAP */
return ret;
--
2.7.4
