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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 7AB9BC433E0 for ; Mon, 18 May 2020 16:52:31 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3747120674 for ; Mon, 18 May 2020 16:52:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="AlS1SArS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3747120674 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=P575x9v/EyaMqvJl6E8AQBiLdAl+HpE25ilnwtFLY3A=; b=AlS1SArSA/T1ub YR4LflqzZQabLq+jBzOMUH8KuSbk0Qbo+K8ZwawdoqCXZtOXPbs9s9N2+08KmcvFanB8kLDyTsKDr hU0ZULx6NxGppvvAAiCn3bXJP0xsacI+mIW79xcheThdh5MyTQHFPloXMIO3fKfA421AjUlWFdeZ7 /ul8eXvqiiaoiXQPloIyFJ9pTwjsVEHaLxP2oAq43eMGGKQCUBrDpDuGDjvqIPX/RZa0uVIlzi+Qv i0x3aJOLalL4zweOUXOJFZIlgLCXTIHkDVMQXJ5Euf6QLfS3+dvT17d2aGOOK5OOBNFIMRClNob8O pidJEKFtf6/HcljjqRJQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jaj0A-0000cK-Nz; Mon, 18 May 2020 16:52:30 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jaj07-0000bn-Oh for linux-arm-kernel@lists.infradead.org; Mon, 18 May 2020 16:52:29 +0000 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 1A1D3106F; Mon, 18 May 2020 09:52:27 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7EE723F305; Mon, 18 May 2020 09:52:25 -0700 (PDT) Date: Mon, 18 May 2020 17:52:23 +0100 From: Dave Martin To: Szabolcs Nagy Subject: Re: [PATCH v3 23/23] arm64: mte: Add Memory Tagging Extension documentation Message-ID: <20200518165223.GB5031@arm.com> References: <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> <20200515125332.GF27289@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200515125332.GF27289@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200518_095227_845194_DACF5685 X-CRM114-Status: GOOD ( 21.36 ) 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: linux-arch@vger.kernel.org, Richard Earnshaw , Vincenzo Frascino , Peter Collingbourne , Catalin Marinas , Kevin Brodsky , linux-mm@kvack.org, Andrey Konovalov , nd@arm.com, Will Deacon , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; 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 On Fri, May 15, 2020 at 01:53:32PM +0100, Szabolcs Nagy wrote: > 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. Hmmm, I guess this might eventually be wanted. But it's probably OK not to have it to begin with. Things like CRIU restores won't be reproducible unless the seeds can be saved/restored. Doesn't seem essential from day 1 though. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel