linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Add early memory allocation errata

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Message-ID: <20181005151505.GO3795@rric.localdomain>
Date:   Fri, 5 Oct 2018 15:15:14 +0000
From:   "Richter, Robert" <Robert.Richter@...ium.com>
To:     Matthias Brugger <matthias.bgg@...il.com>
CC:     Marc Zyngier <marc.zyngier@....com>,
        Matthias Brugger <mbrugger@...e.com>,
        "matthias.bgg@...nel.org" <matthias.bgg@...nel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "jason@...edaemon.net" <jason@...edaemon.net>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        "shankerd@...eaurora.org" <shankerd@...eaurora.org>,
        "xiexiuqi@...wei.com" <xiexiuqi@...wei.com>,
        "Dave.Martin@....com" <Dave.Martin@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irqchip/gic-v3-its: Add early memory allocation errata

On 05.10.18 16:13:48, Matthias Brugger wrote:
> On 05/10/2018 15:42, Marc Zyngier wrote:
> > On 05/10/18 13:33, Matthias Brugger wrote:

> >> With my distribution head on, I would prefer a solution that does not change
> >> FORCE_MAX_ZONEORDER. That's how I came to the idea providing a third solution to
> >> the same problem :)
> >
> > Why is that a problem? What impact does this have on your favourite distro?
> >
> 
> The impact is on changing FORCE_MAX_ZONEORDER on an already released kernel will
> break Kernel ABI and with that all external modules. I know that's nothing
> upstream cares too much about, but the distros do :)

Wrt upstream, there is no way to do this change without patching the
kernel. Thus, it is impossible to run an unpatched 4k page size kernel
on ThunderX.

-Robert