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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:60362) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1hlrLc-0000p6-7n; Fri, 12 Jul 2019 09:56:08 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.89) (envelope-from ) id 1hlrLX-0005XL-2W; Fri, 12 Jul 2019 09:56:03 +0100 Date: Fri, 12 Jul 2019 09:56:02 +0100 From: Russell King - ARM Linux admin To: "Raslan, KarimAllah" Subject: Re: [PATCH] arm: Extend the check for RAM in /dev/mem Message-ID: <20190712085602.v2tncu5tsngtvbww@shell.armlinux.org.uk> References: <1562883681-18659-1-git-send-email-karahmed@amazon.de> <14f02e29-77b2-29d9-a9f4-7f89ad0194f6@arm.com> <1562900298.1345.12.camel@amazon.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1562900298.1345.12.camel@amazon.de> User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190712_015826_147541_8C6509F2 X-CRM114-Status: GOOD ( 13.03 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "mark.rutland@arm.com" , "anders.roxell@linaro.org" , "yuzhao@google.com" , "will@kernel.org" , "ard.biesheuvel@linaro.org" , "info@metux.net" , "anshuman.khandual@arm.com" , "linux-kernel@vger.kernel.org" , "rppt@linux.ibm.com" , "yaojun8558363@gmail.com" , "james.morse@arm.com" , "catalin.marinas@arm.com" , "tglx@linutronix.de" , "robin.murphy@arm.com" , "akpm@linux-foundation.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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=3D ker= nel > > > command-line). For these regions, pfn_valid would return "false" caus= ing > > > 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=3D command line) what is the particular concern regar= ding > > 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= =A0 > kernel. One use-case would be using them as guest memory for KVM as I det= ailed=A0 > 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. -- = RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps = up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel