Messages in this thread | | | Date | Thu, 2 Feb 2023 11:09:26 +0100 | From | Christoph Hellwig <> | Subject | Re: Regression: v4l/bttv vbi vs iommu |
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On Wed, Feb 01, 2023 at 04:26:42PM +0000, Dr. David Alan Gilbert wrote: > f5ff79fddf0efecca538046b5cc20fb3ded2ec4f is the first bad commit > commit f5ff79fddf0efecca538046b5cc20fb3ded2ec4f > Author: Christoph Hellwig <hch@lst.de> > Date: Sat Feb 26 16:40:21 2022 +0100 > > dma-mapping: remove CONFIG_DMA_REMAP
Which just enabled some code on common x86 configs that was already used on many other platforms. In other words: the code already was buggy, but got away with it on x86 so far as no one tested on e.g. arm or arm64.
The bug is in videobuf_dma_init_kernel:
for (i = 0; i < nr_pages; i++) { void *addr;
addr = dma_alloc_coherent(dma->dev, PAGE_SIZE, &(dma->dma_addr[i]), GFP_KERNEL); if (addr == NULL) goto out_free_pages;
dma->vaddr_pages[i] = virt_to_page(addr); } dma->vaddr = vmap(dma->vaddr_pages, nr_pages, VM_MAP | VM_IOREMAP, PAGE_KERNEL);
The address by dma_alloc_coherent is just a kernel virtual address, and virt_to_page must not be used on it as it could be vmalloc (as in this case) or various other really odd forms of memory.
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