From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97EFFC433E0 for ; Fri, 15 May 2020 12:13:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5E95C20657 for ; Fri, 15 May 2020 12:13:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5E95C20657 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id EC0D490000C; Fri, 15 May 2020 08:13:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E70E18E0005; Fri, 15 May 2020 08:13:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D5DF490000C; Fri, 15 May 2020 08:13:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0198.hostedemail.com [216.40.44.198]) by kanga.kvack.org (Postfix) with ESMTP id BCC268E0005 for ; Fri, 15 May 2020 08:13:53 -0400 (EDT) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 787E1181AEF00 for ; Fri, 15 May 2020 12:13:53 +0000 (UTC) X-FDA: 76818844746.02.toe92_793c253119452 X-HE-Tag: toe92_793c253119452 X-Filterd-Recvd-Size: 2897 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf28.hostedemail.com (Postfix) with ESMTP for ; Fri, 15 May 2020 12:13:52 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 019C11042; Fri, 15 May 2020 05:13:52 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 56B4B3F305; Fri, 15 May 2020 05:13:50 -0700 (PDT) Date: Fri, 15 May 2020 13:13:44 +0100 From: Catalin Marinas To: Szabolcs Nagy 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: <20200515121343.GC22393@gaia> References: <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> <20200515120433.GE27289@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200515120433.GE27289@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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). -- Catalin