linux-kernel - Re: ARM: static kernel in vmalloc space

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Message-ID: <CAK8P3a2KR+O5Ua5hsNgzLQV5-V1pat6JH_WM10Es-oUhXO2OgA@mail.gmail.com>
Date:   Thu, 14 May 2020 23:12:01 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     afzal mohammed <afzal.mohd.ma@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: ARM: static kernel in vmalloc space

On Thu, May 14, 2020 at 6:25 PM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
> On Thu, May 14, 2020 at 02:41:11PM +0200, Arnd Bergmann wrote:
> > On Thu, May 14, 2020 at 1:18 PM afzal mohammed <afzal.mohd.ma@...il.com> wrote:

> > It's clearly possible to do something very similar for older chips
> > (v6 or v7 without LPAE, possibly even v5), it just gets harder
> > while providing less benefit.
>
> Forget about doing this for anything without a PIPT cache - or you're
> going to end up having to flush the data cache each time you enter or
> exit the kernel.

Right, let's forget I said anything about v5 or earlier ;-)

I expected the non-aliasing VIPT caches to work the same as PIPT, can
you clarify if there is something to be aware of for those? I see that some
ARMv8 chips and most ARMv6 chips (not OMAP2 and Realview) are
of that kind, and at we clearly don't want to break running on ARMv8 at
least.

Anyway my point was that it's best to only do it for LPAE anyway, everything
else being a distraction, as the only non-LPAE SoCs I could find with
support for over 2GB are some of the higher-end i.MX6 versions and the
original highbank.

      Arnd