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

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Message-ID: <20200514234013.GQ1551@shell.armlinux.org.uk>
Date:   Fri, 15 May 2020 00:40:14 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Arnd Bergmann <arnd@...db.de>
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 11:12:01PM +0200, Arnd Bergmann wrote:
> 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.

There are some aliasing VIPT implementations on ARMv6, but I don't
remember how common.

> 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.

Yep.

-- 
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