On Wednesday 02 July 2014, Laura Abbott wrote:
> + pgprot_t prot = __pgprot(PROT_NORMAL_NC);
> + unsigned long nr_pages = atomic_pool_size >> PAGE_SHIFT;
> + struct page *page;
> + void *addr;
> +
> +
> + if (dev_get_cma_area(NULL))
> + page = dma_alloc_from_contiguous(NULL, nr_pages,
> + get_order(atomic_pool_size));
> + else
> + page = alloc_pages(GFP_KERNEL, get_order(atomic_pool_size));
> +
> +
> + if (page) {
> + int ret;
> +
> + atomic_pool = gen_pool_create(PAGE_SHIFT, -1);
> + if (!atomic_pool)
> + goto free_page;
> +
> + addr = dma_common_contiguous_remap(page, atomic_pool_size,
> + VM_USERMAP, prot, atomic_pool_init);
> +
I just stumbled over this thread and noticed the code here: When you do
alloc_pages() above, you actually get pages that are already mapped into
the linear kernel mapping as cacheable pages. Your new
dma_common_contiguous_remap tries to map them as noncacheable. This
seems broken because it allows the CPU to treat both mappings as
cacheable, and that won't be coherent with device DMA.
> + if (!addr)
> + goto destroy_genpool;
> +
> + memset(addr, 0, atomic_pool_size);
> + __dma_flush_range(addr, addr + atomic_pool_size);
It also seems weird to flush the cache on a virtual address of
an uncacheable mapping. Is that well-defined? In the CMA case, the
original mapping should already be uncached here, so you don't need
to flush it. In the alloc_pages() case, I think you need to unmap
the pages from the linear mapping instead.
Arnd
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