linux-kernel - Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC

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Date:   Fri, 30 Sep 2022 12:35:45 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Isaac Manjarres <isaacmanjarres@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Saravana Kannan <saravanak@...gle.com>, kernel-team@...roid.com
Subject: Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN

On Fri, Sep 30, 2022 at 11:33 AM Catalin Marinas
<catalin.marinas@....com> wrote:
>
> I started refreshing the series but I got stuck on having to do bouncing
> for small buffers even if when they go through the iommu (and I don't
> have the set up to test it yet).

May I suggest doing that "force bouncing" and "change kmalloc to have
a 8-byte minalign" to be the two first commits?

IOW, if we force bouncing for unaligned DMA, then that *should* mean
that allocation alignment is no longer a correctness issue, it's
purely a performance one due to the bouncing.

So then the rest of the series should be about "ok, this is actually a
hot enough allocation that I want to force alignment", and be purely
about performance, not correctness.

No?

               Linus