On Fri, Apr 15, 2022 at 12:22:27PM +0200, Ard Biesheuvel wrote: > > Subsequent objects are owned by the driver, and it is the > responsibility of the driver not to modify the fields while it is also > mapped for DMA (and we have had issues in the past where drivers > violated this rule). So as long as ARCH_KMALLOC_ALIGN guarantees > actual DMA minimum alignment for both the start and the end, we > shouldn't need any explicit padding at the end. I don't understand why this is guaranteed. The driver context size is arbitrary so it could end in the middle of a cacheline. The slab allocator could well lay it out so that the next kmalloc object starts right after the end of the context, in which case they would share a cache-line. The next kmalloc object could be (and in fact is likely to be) of the same type. Previously this wasn't possible because kmalloc guaranteed alignment. > I'l do a scan of drivers/crypto to figure out how much we are relying > on this to begin with. Thanks, -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
