On Fri, Apr 19, 2024 at 09:30:07AM -0700, Eric Biggers wrote: > > If you mean the fallback to scalar instructions when !crypto_simd_usable(), by > default dm-verity and fs-verity do all hashing in process context, in which case > the scalar fallback will never be used. dm-verity does support the > 'try_verify_in_tasklet' option which makes hashing sometimes happen in softirq > context, and x86 Linux has an edge case where if a softirq comes in while the > kernel is in the middle of using SIMD instructions, SIMD instructions can't be > used during that softirq. So in theory the !crypto_simd_usable() case could be > reached then. Either way, I have the fallback implemented in the x86 and arm64 > SHA-256 glue code for consistency with the rest of the crypto_shash API anyway. OK that's good to hear. So if they enable try_verify_in_tasklet then they will only have themselves to blame :) > If you mean falling back to two crypto_shash_finup() when the algorithm doesn't > support crypto_shash_finup2x(), my patches to dm-verity and fs-verity do that. > Modern x86_64 and arm64 systems will use crypto_shash_finup2x(), but dm-verity > and fs-verity need to work on all architectures and on older CPUs too. The > alternative would be to put the fallback to two crypto_shash_finup() directly in > crypto_shash_finup2x() and have the users call crypto_shash_finup2x() > unconditionally (similar to how crypto_shash_digest() can be called even if the > underlying shash_alg doesn't implement ->digest()). That would make for > slightly simpler code, though it feels a bit awkward to queue up multiple blocks > for multibuffer hashing when multibuffer hashing won't actually be used. Let me > know if you have a preference about this. No I don't think it's necessary for the time being. Thanks, -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
