[PATCH] arm64: errata: Remove AES hwcap for COMPAT tasks on A57 and A72

[Arnd Bergmann]

On Thu, Jan 27, 2022 at 7:43 PM Robin Murphy <robin.murphy at arm.com> wrote:
> On 2022-01-27 14:52, Arnd Bergmann wrote:
> > On Thu, Jan 27, 2022 at 1:39 PM Ard Biesheuvel <ardb at kernel.org> wrote:
> >> Cortex-A57 and Cortex-A72 have an erratum where an interrupt that
> >> occurs between a pair of AES instructions in aarch32 mode may corrupt
> >> the ELR. The task will subsequently produce the wrong AES result.
> >
> >> Fortunately, the only A72 that is known to be widely deployed with
> >> 32-bit kernels and/or user space is the Raspberry Pi 4, which does not
> >> implement the crypto extensions.
> >
> > I have previously used Amazon EC2 A1 instances (using Graviton 1, Cortex-A72)
> > to run Debian armhf and armel user space in chroot environments. No idea how
> > common that is for production environments, but there is a good chance that
> > actual users might use e.g. 32-bit docker images for Alpine Linux on the same
> > machines.
> >
> > There are also some early A57/A72 chips used in Android devices that may
> > frequently run 32-bit applications, or even be limited to 32-bit
> > kernels, see [1].
> > Not sure how likely it is for any of them to get (a backport of) this
> > patch though.
>
> Isn't ChromeOS still notoriously shipping AArch32 userspace? Between
> Mediatek and Rockchip, both A57 and A72 are definitely playing on that
> stage.

I wouldn't call it "notorious", but indeed that is an important user
that I missed. For some reason I misremembered that both mt8173 and
rk3399 are Cortex-A73 based, but they are A72 as you say.

> I'd concur that 32-bit *kernel* on v8 is a bit of a specialist sport,
> especially these days. IIRC Exynos 5433 might have been one of the more
> common Android setups for that, but 2015 is now an eternity ago in phone
> years..

Unfortunately, 32-bit kernels are still a thing on low-end Android phones,
including some very recent Cortex-A55 based products with Android Go
edition and 2GB of RAM or less, and also some highly popular (at the time)
Cortex-A53 Snapdragon 410 phones started shipping before a 64-bit kernel
port was available on Snapdragon.

A57/A72 at least disappeared from phones a long time ago because of
both cost and power consumption reasons, so it's only the low end devices
now. I'm not aware of any Android devices actually shipping with a 64-bit
kernel and 32-bit user space, maybe that was never an option in the SDK.

        Arnd