On Thu, Mar 12, 2026 at 07:29:05PM -0400, Mimi Zohar wrote: > On Wed, 2026-03-11 at 22:39 -0700, Eric Biggers wrote: > > IMA computes hashes using the crypto_shash or crypto_ahash API. The > > latter is used only when ima.ahash_minsize is set on the command line, > > and its purpose is ostensibly to make the hash computation faster. > > > > However, going off the CPU to a crypto engine and back again is actually > > quite slow, especially compared with the acceleration that is built into > > modern CPUs and the kernel now enables by default for most algorithms. > > Typical performance results for SHA-256 on a modern platform can be > > found at https://lore.kernel.org/linux-crypto/20250615184638.GA1480@sol/ > > > > Partly for this reason, several other kernel subsystems have already > > dropped support for the crypto_ahash API. > > The performance benefit was the ability of reading and filling a buffer from > disk, which was slow, while the other buffer was sent to the crypto engine.
On normal filesystems, sequential reads from a file already kick off async readahead. So the hashing and disk reads can already happen concurrently anyway. - Eric
