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 [off-list ref]
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel