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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D1C19C433FE for ; Wed, 11 May 2022 07:23:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6014E6B0073; Wed, 11 May 2022 03:23:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5B1AA6B0075; Wed, 11 May 2022 03:23:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4A0A36B0078; Wed, 11 May 2022 03:23:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 3C97D6B0073 for ; Wed, 11 May 2022 03:23:17 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay11.hostedemail.com (Postfix) with ESMTP id 1D77381E33 for ; Wed, 11 May 2022 07:23:17 +0000 (UTC) X-FDA: 79452621234.02.A63CE9F Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf08.hostedemail.com (Postfix) with ESMTP id 0BD51160094 for ; Wed, 11 May 2022 07:23:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=mX/LPDRiM2kjAACGQpTgwsVpipKtiyAP/j4T+KMpNkM=; b=H2/3L8F7yOeN39Y9I52eNdrzPI 6WJJqorodqUEV1tadzEdsg+pmg6ApMstzoETm5LYfYIBf3jRFe8ZM1oLQaOn9g5/nU+BYx+jZmCtV ApK+n2Bs6quvnCfX3491X21sptzS+5fRS7wH70EJWI3PM9Vr6l8PHIFBC41q+6VGbMKkzmqzVSSIh TJCgpvJIGzzZw7tB91z4c6ujByRcMa6t3HzePMVu95nTb6jdQkB5t2CSmI6cNNONuOmEEWC8gbhen 5hWhj7bZa6MMBdMpkYJ0YtnTQ/ORRuQeE0mXNJ7dfgu9vJCcxc+9kX7K9Le2UDRskwC0u73X4T4p2 WSpasbIA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1noggg-005EEx-Kt; Wed, 11 May 2022 07:23:10 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 445C3980E3A; Wed, 11 May 2022 09:23:10 +0200 (CEST) Date: Wed, 11 May 2022 09:23:10 +0200 From: Peter Zijlstra To: "Kirill A. Shutemov" Cc: Dave Hansen , Andy Lutomirski , x86@kernel.org, Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFCv2 07/10] x86/mm: Handle tagged memory accesses from kernel threads Message-ID: <20220511072310.GU76023@worktop.programming.kicks-ass.net> References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com> <20220511022751.65540-9-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220511022751.65540-9-kirill.shutemov@linux.intel.com> X-Stat-Signature: nruadon68jxm913kmpp17mnmhwneiben X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0BD51160094 X-Rspam-User: Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="H2/3L8F7"; dmarc=none; spf=none (imf08.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org X-HE-Tag: 1652253782-964191 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 Wed, May 11, 2022 at 05:27:48AM +0300, Kirill A. Shutemov wrote: > When a kernel thread performs memory access on behalf of a process (like > in async I/O, io_uring, etc.) it has to respect tagging setup of the > process as user addresses can include tags. > > Normally, LAM setup is per-thread and recorded in thread features, but > for this use case kernel also tracks LAM setup per-mm. mm->context.lam > would record LAM that allows the most tag bits among the threads of > the mm. Then why does it *ever* make sense to track it per thread? It's not like it makes heaps of sense to allow one thread in a process to use LAM but not the others.