diff options
| author | Yosry Ahmed <yosryahmed@google.com> | 2024-08-10 00:59:11 +0000 |
|---|---|---|
| committer | Christoph Hellwig <hch@lst.de> | 2024-08-22 06:15:35 +0200 |
| commit | fa3c109a6d302b56437a6412c5f3044c3e12de03 (patch) | |
| tree | 8d1556ff2886e98466589c2cb61a92093e871f16 | |
| parent | 47ac09b91befbb6a235ab620c32af719f8208399 (diff) | |
dma-mapping: use bit masking to check VM_DMA_COHERENT
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>
| -rw-r--r-- | kernel/dma/remap.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/dma/remap.c b/kernel/dma/remap.c index 27596f3b4aef..9e2afad1c615 100644 --- a/kernel/dma/remap.c +++ b/kernel/dma/remap.c @@ -10,8 +10,10 @@ struct page **dma_common_find_pages(void *cpu_addr) { struct vm_struct *area = find_vm_area(cpu_addr); - if (!area || area->flags != VM_DMA_COHERENT) + if (!area || !(area->flags & VM_DMA_COHERENT)) return NULL; + WARN(area->flags != VM_DMA_COHERENT, + "unexpected flags in area: %p\n", cpu_addr); return area->pages; } @@ -61,7 +63,7 @@ void dma_common_free_remap(void *cpu_addr, size_t size) { struct vm_struct *area = find_vm_area(cpu_addr); - if (!area || area->flags != VM_DMA_COHERENT) { + if (!area || !(area->flags & VM_DMA_COHERENT)) { WARN(1, "trying to free invalid coherent area: %p\n", cpu_addr); return; } |