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Fri, 15 May 2020 12:53:44 +0000 Date: Fri, 15 May 2020 13:53:32 +0100 From: Szabolcs Nagy To: Catalin Marinas Subject: Re: [PATCH v3 23/23] arm64: mte: Add Memory Tagging Extension documentation Message-ID: <20200515125332.GF27289@arm.com> References: <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> <20200515120433.GE27289@arm.com> <20200515121343.GC22393@gaia> Content-Disposition: inline In-Reply-To: <20200515121343.GC22393@gaia> User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: SN6PR08CA0021.namprd08.prod.outlook.com (2603:10b6:805:66::34) 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 SN6PR08CA0021.namprd08.prod.outlook.com (2603:10b6:805:66::34) 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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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org The 05/15/2020 13:13, Catalin Marinas wrote: > On Fri, May 15, 2020 at 01:04:33PM +0100, Szabolcs Nagy wrote: > > The 05/15/2020 12:27, Catalin Marinas wrote: > > > Thanks Szabolcs. 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. > > Yes, that's the implementation specific algorithm which shouldn't be > worse than the standard one. > > > > 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. > > It generates a random tag based on some algorithm. > > > 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)? > > The seed is only relevant if the standard algorithm is used (RRND=0). i wanted to understand if we can get deterministic irg behaviour in user space (which may be useful for debugging to get reproducible tag failures). i guess if no control is exposed that means non- deterministic irg. i think this is fine. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel