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

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Date:   Thu, 6 Jan 2022 17:25:34 +0100
From:   Milan Broz <gmazyland@...il.com>
To:     "Bae, Chang Seok" <chang.seok.bae@...el.com>
Cc:     "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Krishnakumar, Lalithambika" <lalithambika.krishnakumar@...el.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        "Lutomirski, Andy" <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...nel.org>,
        "Gairuboyina, Charishma1" <charishma1.gairuboyina@...el.com>,
        "Dwarakanath, Kumar N" <kumar.n.dwarakanath@...el.com>,
        Eric Biggers <ebiggers@...nel.org>
Subject: Re: [dm-devel] [PATCH v4 00/13] x86: Support Key Locker

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