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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Tue, 16 Mar 2021 13:35:40 +0100
Message-ID: <CAMj1kXHzEEU2-mVxVD8g=P_Py_WJMOn0q8m+k-txUUioS+2ajQ@mail.gmail.com>
Subject: Re: stable request
To:     Thomas Backlund <tmb@tmb.nu>
Cc:     "# 3.4.x" <stable@vger.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Eric Biggers <ebiggers@kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>
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On Tue, 16 Mar 2021 at 13:28, Thomas Backlund <tmb@tmb.nu> wrote:
>
>
> Den 16.3.2021 kl. 14:15, skrev Thomas Backlund:
> >
> > Den 16.3.2021 kl. 12:17, skrev Ard Biesheuvel:
> >> On Tue, 16 Mar 2021 at 10:21, Thomas Backlund <tmb@tmb.nu> wrote:
> >>> Den 16.3.2021 kl. 08:37, skrev Ard Biesheuvel:
> >>>> Please consider backporting commit
> >>>>
> >>>> 86ad60a65f29dd862a11c22bb4b5be28d6c5cef1
> >>>> crypto: x86/aes-ni-xts - use direct calls to and 4-way stride
> >>>>
> >>>> to stable. It addresses a rather substantial retpoline-related
> >>>> performance regression in the AES-NI XTS code, which is a widely used
> >>>> disk encryption algorithm on x86.
> >>>>
> >>> To get all the nice bits, we added the following in Mageia 5.10 / 5.11
> >>> series kerenels (the 2 first is needed to get the third to apply/build
> >>> nicely):
> >>>
> >> I will leave it up to the -stable maintainers to decide, but I will
> >> point out that none of the additional patches fix any bugs, so this
> >> may violate the stable kernel rules. In fact, I deliberately split the
> >> XTS changes into two  patches so that the first one could be
> >> backported individually.
> >
> > Yes, I understand that.
> >
> > but commit
> >
> > 86ad60a65f29dd862a11c22bb4b5be28d6c5cef1
> > crypto: x86/aes-ni-xts - use direct calls to and 4-way stride
> >
> > only applies cleanly on 5.11.
> >
> >
> > So if it's wanted in 5.10 you need the 2 others too... unless you intend to provide a tested backport...
> > and IIRC GregKH prefers 1:1 matching of patches between -stable and linus tree unless they are too intrusive.
> >
> >
> > As for the last one I seem to remember comments that it too was part of the "affects performance", but I might be remembering wrong... and since you are Author of them I assume you know better about the facts :)
> >
> >
> > That's why I listed them as an extra "hopefully helfpful" info and datapoint that they work...
> > We have been carrying them in 5.10 series since we rebased to 5.10.8 on January 17th, 2021
> >
> >
> > but in the end it's up to the -stable maintainers as you point out...
>
>
> and now  I re-checked...
>
> Only the first is needed to get your fix to apply cleanly on 5.10
>
>
> the second came in as a pre-req for the fourth patch...
>

OK so that would be

032d049ea0f45b45c21f3f02b542aa18bc6b6428
Uros Bizjak <ubizjak@gmail.com>
crypto: aesni - Use TEST %reg,%reg instead of CMP $0,%reg

which is already in 5.11, but needs to be backported as well for the
originally requested backport to apply cleanly to 5.10 and earlier.

Thanks for digging that up.

-- 
Ard.