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In dma_common_find_pages(), area->flags are compared directly with VM_DMA_COHERENT. This works because VM_DMA_COHERENT is the only set flag. During development of a new feature (ASI [1]), a new VM flag is introduced, and that flag can be injected into VM_DMA_COHERENT mappings (among others). The presence of that flag caused dma_common_find_pages() to return NULL for VM_DMA_COHERENT addresses, leading to a lot of problems ending in crashing during boot. It took a bit of time to figure this problem out. It was a mistake to inject a VM flag to begin with, but it took a significant amount of debugging to figure out the problem. Most users of area->flags use bitmasking rather than equivalency to check for flags. Update dma_common_find_pages() and dma_common_free_remap() to do the same, which would have avoided the boot crashing. Instead, add a warning in dma_common_find_pages() if any extra VM flags are set to catch such problems more easily during development. No functional change intended. [1]https://lore.kernel.org/lkml/20240712-asi-rfc-24-v1-0-144b319a40d8@google.com/ Signed-off-by: Yosry Ahmed <yosryahmed@google.com> Signed-off-by: Christoph Hellwig <hch@lst.de>
73 lines
1.7 KiB
C
73 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (c) 2014 The Linux Foundation
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*/
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#include <linux/dma-map-ops.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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struct page **dma_common_find_pages(void *cpu_addr)
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{
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struct vm_struct *area = find_vm_area(cpu_addr);
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if (!area || !(area->flags & VM_DMA_COHERENT))
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return NULL;
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WARN(area->flags != VM_DMA_COHERENT,
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"unexpected flags in area: %p\n", cpu_addr);
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return area->pages;
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}
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/*
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* Remaps an array of PAGE_SIZE pages into another vm_area.
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* Cannot be used in non-sleeping contexts
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*/
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void *dma_common_pages_remap(struct page **pages, size_t size,
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pgprot_t prot, const void *caller)
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{
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void *vaddr;
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vaddr = vmap(pages, PAGE_ALIGN(size) >> PAGE_SHIFT,
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VM_DMA_COHERENT, prot);
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if (vaddr)
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find_vm_area(vaddr)->pages = pages;
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return vaddr;
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}
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/*
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* Remaps an allocated contiguous region into another vm_area.
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* Cannot be used in non-sleeping contexts
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*/
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void *dma_common_contiguous_remap(struct page *page, size_t size,
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pgprot_t prot, const void *caller)
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{
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int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
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struct page **pages;
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void *vaddr;
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int i;
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pages = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
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if (!pages)
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return NULL;
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for (i = 0; i < count; i++)
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pages[i] = nth_page(page, i);
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vaddr = vmap(pages, count, VM_DMA_COHERENT, prot);
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kvfree(pages);
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return vaddr;
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}
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/*
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* Unmaps a range previously mapped by dma_common_*_remap
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*/
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void dma_common_free_remap(void *cpu_addr, size_t size)
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{
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struct vm_struct *area = find_vm_area(cpu_addr);
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if (!area || !(area->flags & VM_DMA_COHERENT)) {
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WARN(1, "trying to free invalid coherent area: %p\n", cpu_addr);
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return;
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}
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vunmap(cpu_addr);
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}
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