Re: [dm-devel] [PATCH v4 00/13] x86: Support Key Locker

[Milan Broz]

On 06/01/2022 06:07, Eric Biggers wrote:
> On Wed, Jan 05, 2022 at 09:55:17PM +0000, Bae, Chang Seok wrote:
> > > > +-----------+---------------+---------------+
> > > > | Cipher    |   Encryption  | Decryption    |
> > > > | (AES-KL)  |    (MiB/s)    | (MiB/s)       |
> > > > +-----------+---------------+---------------+
> > > > | AES-CBC   |     505.3     |   2097.8      |
> > > > | AES-XTS   |     1130      |   696.4       |
> > > > +-----------+-------------------------------+
> > >
> > > Why is AES-XTS decryption so much slower than AES-XTS encryption?  They should
> > > be about the same.
> >
> > Analyzing and understanding this with specific hardware implementation takes
> > time for us. Will come back and update you when we have anything to share here.
>
> Note that for disk encryption, decryption performance is usually more important
> than encryption performance.  So your performance results are strange.

If the test results are from "cryptsetup benchmark", it just run benchmark
through userspace crypto API (AF_ALG) - no dm-crypt is involved at all.

Proper test with dm-crypt should be run to get some numbers too.

(But the test results are really strange... there is no reason
decryption should be slower for XTS.)

Also you mention that
> Bare metal disk encryption is the only use case intended by these patches.
> Userspace usage is not supported because there is no ABI provided to
> communicate and coordinate wrapping-key restore failures to userspace.

The cryptsetup benchmark is userspace use (just with kernel netlink
access to kernel crypto). So I am not sure if these number are so important.

Milan