From: "Raslan, KarimAllah" <karahmed@amazon.de>
To: "linux@armlinux.org.uk" <linux@armlinux.org.uk>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>,
"anders.roxell@linaro.org" <anders.roxell@linaro.org>,
"yuzhao@google.com" <yuzhao@google.com>,
"will@kernel.org" <will@kernel.org>,
"ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
"info@metux.net" <info@metux.net>,
"anshuman.khandual@arm.com" <anshuman.khandual@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"rppt@linux.ibm.com" <rppt@linux.ibm.com>,
"yaojun8558363@gmail.com" <yaojun8558363@gmail.com>,
"james.morse@arm.com" <james.morse@arm.com>,
"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"robin.murphy@arm.com" <robin.murphy@arm.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] arm: Extend the check for RAM in /dev/mem
Date: Fri, 12 Jul 2019 08:59:59 +0000 [thread overview]
Message-ID: <1562921998.1345.15.camel@amazon.de> (raw)
In-Reply-To: <20190712085602.v2tncu5tsngtvbww@shell.armlinux.org.uk>
On Fri, 2019-07-12 at 09:56 +0100, Russell King - ARM Linux admin wrote:
> On Fri, Jul 12, 2019 at 02:58:18AM +0000, Raslan, KarimAllah wrote:
> >
> > On Fri, 2019-07-12 at 08:06 +0530, Anshuman Khandual wrote:
> > >
> > >
> > > On 07/12/2019 03:51 AM, KarimAllah Ahmed wrote:
> > > >
> > > >
> > > > Some valid RAM can live outside kernel control (e.g. using mem= kernel
> > > > command-line). For these regions, pfn_valid would return "false" causing
> > > > system RAM to be mapped as uncached. Use memblock instead to identify RAM.
> > >
> > > Once the remaining memory is outside of the kernel (as the admin would have
> > > intended with mem= command line) what is the particular concern regarding
> > > the way those get mapped (cached or not) ? It is not to be used any way.
> >
> > They can be used by user-space which might lead to them being used by the
> > kernel. One use-case would be using them as guest memory for KVM as I detailed
> > here:
> >
> > https://lwn.net/Articles/778240/
>
> From the 32-bit ARM point of view...
>
> What if someone's already doing something similar with a non-coherent
> DSP and is relying on the current behaviour? This change is a user
> visible behavioural change that could end up breaking userspace.
>
> In other words, it isn't something we should rush into.
Yes, that makes sense. How about adding a command-line option for this new
behavior instead? Would this be more reasonable?
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next prev parent reply other threads:[~2019-07-12 9:00 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 22:21 [PATCH] arm: Extend the check for RAM in /dev/mem KarimAllah Ahmed
2019-07-12 2:36 ` Anshuman Khandual
2019-07-12 2:58 ` Raslan, KarimAllah
2019-07-12 8:56 ` Russell King - ARM Linux admin
2019-07-12 8:59 ` Raslan, KarimAllah [this message]
2019-07-12 14:57 ` Will Deacon
2019-07-12 15:13 ` Raslan, KarimAllah
2019-07-12 15:34 ` Will Deacon
2019-07-12 15:46 ` Raslan, KarimAllah
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