dma-mapping: fix page attributes for dma_mmap_*

All the way back to introducing dma_common_mmap we've defaulted to mark
the pages as uncached.  But this is wrong for DMA coherent devices.
Later on DMA_ATTR_WRITE_COMBINE also got incorrect treatment as that
flag is only treated special on the alloc side for non-coherent devices.

Introduce a new dma_pgprot helper that deals with the check for coherent
devices so that only the remapping cases ever reach arch_dma_mmap_pgprot
and we thus ensure no aliasing of page attributes happens, which makes
the powerpc version of arch_dma_mmap_pgprot obsolete and simplifies the
remaining ones.

Note that this means arch_dma_mmap_pgprot is a bit misnamed now, but
we'll phase it out soon.

Fixes: 64ccc9c033c6 ("common: dma-mapping: add support for generic dma_mmap_* calls")
Reported-by: Shawn Anastasio <shawn@anastas.io>
Reported-by: Gavin Li <git@thegavinli.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com> # arm64

1 files changed, 18 insertions, 1 deletions

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index b945239621d8..b0038ca3aa92 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -150,6 +150,23 @@ int dma_get_sgtable_attrs(struct device *dev, struct sg_table *sgt,
 }
 EXPORT_SYMBOL(dma_get_sgtable_attrs);
 
+#ifdef CONFIG_MMU
+/*
+ * Return the page attributes used for mapping dma_alloc_* memory, either in
+ * kernel space if remapping is needed, or to userspace through dma_mmap_*.
+ */
+pgprot_t dma_pgprot(struct device *dev, pgprot_t prot, unsigned long attrs)
+{
+        if (dev_is_dma_coherent(dev) ||
+            (IS_ENABLED(CONFIG_DMA_NONCOHERENT_CACHE_SYNC) &&
+             (attrs & DMA_ATTR_NON_CONSISTENT)))
+                return prot;
+        if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_MMAP_PGPROT))
+                return arch_dma_mmap_pgprot(dev, prot, attrs);
+        return pgprot_noncached(prot);
+}
+#endif /* CONFIG_MMU */
+
 /*
  * Create userspace mapping for the DMA-coherent memory.
  */
@@ -164,7 +181,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
         unsigned long pfn;
         int ret = -ENXIO;
 
-        vma->vm_page_prot = arch_dma_mmap_pgprot(dev, vma->vm_page_prot, attrs);
+        vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, attrs);
 
         if (dma_mmap_from_dev_coherent(dev, vma, cpu_addr, size, &ret))
                 return ret;