Messages in this thread | | | Subject | Re: block: DMA alignment of IO buffer allocated from slab | From | Bart Van Assche <> | Date | Mon, 24 Sep 2018 09:19:44 -0700 |
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On Mon, 2018-09-24 at 19:07 +0300, Andrey Ryabinin wrote: > On 09/24/2018 06:58 PM, Bart Van Assche wrote: > > On Mon, 2018-09-24 at 18:52 +0300, Andrey Ryabinin wrote: > > > Yes, with CONFIG_DEBUG_SLAB=y, CONFIG_SLUB_DEBUG_ON=y kmalloc() guarantees > > > that result is aligned on ARCH_KMALLOC_MINALIGN boundary. > > > > Had you noticed that Vitaly Kuznetsov showed that this is not the case? See > > also https://lore.kernel.org/lkml/87h8ij0zot.fsf@vitty.brq.redhat.com/. > > I'm not following. On x86-64 ARCH_KMALLOC_MINALIGN is 8, all pointers that > Vitaly Kuznetsov showed are 8-byte aligned.
Hi Andrey,
That means that two buffers allocated with kmalloc() may share a cache line on x86-64. Since it is allowed to use a buffer allocated by kmalloc() for DMA, can this lead to data corruption, e.g. if the CPU writes into one buffer allocated with kmalloc() and a device performs a DMA write to another kmalloc() buffer and both write operations affect the same cache line?
Thanks,
Bart.
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