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Fri, 15 May 2020 12:04:35 +0000 Date: Fri, 15 May 2020 13:04:33 +0100 From: Szabolcs Nagy To: Catalin Marinas Cc: Dave Martin , linux-arch@vger.kernel.org, Richard Earnshaw , Andrey Konovalov , Kevin Brodsky , Peter Collingbourne , linux-mm@kvack.org, Vincenzo Frascino , Will Deacon , linux-arm-kernel@lists.infradead.org, nd@arm.com Subject: Re: [PATCH v3 23/23] arm64: mte: Add Memory Tagging Extension documentation Message-ID: <20200515120433.GE27289@arm.com> References: <20200421142603.3894-24-catalin.marinas@arm.com> <20200429164705.GF30377@arm.com> <20200430162316.GJ2717@gaia> <20200504164617.GK30377@arm.com> <20200511164018.GC19176@gaia> <20200513154845.GT21779@arm.com> <20200514113722.GA1907@gaia> <20200515103839.GA22393@gaia> <20200515111359.GC27289@arm.com> <20200515112740.GB22393@gaia> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200515112740.GB22393@gaia> User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: LO2P265CA0344.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:d::20) To AM6PR08MB3047.eurprd08.prod.outlook.com (2603:10a6:209:4c::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from arm.com (217.140.106.55) by LO2P265CA0344.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:d::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3000.20 via Frontend Transport; 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While we are at this, no-one so far asked for the > GCR_EL1.RRND to be exposed to user (and this implies RGSR_EL1.SEED). > Since RRND=1 guarantees a distribution "no worse" than that of RRND=0, I > thought there isn't much point in exposing this configuration to the > user. The only advantage of RRND=0 I see is that the kernel can change it seems RRND=1 is the impl specific algorithm. > the seed randomly but, with only 4 bits per tag, it really doesn't > matter much. > > Anyway, mentioning it here in case anyone is surprised later about the > lack of RRND configurability. i'm not familiar with how irg works. is the seed per process state that's set up at process startup in some way? or shared (and thus effectively irg is non-deterministic in userspace)?