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 B7945C3DA4A for ; Mon, 19 Aug 2024 11:46:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 52F8C6B007B; Mon, 19 Aug 2024 07:46:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 505946B0082; Mon, 19 Aug 2024 07:46:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 41BCE6B008A; Mon, 19 Aug 2024 07:46:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 249896B007B for ; Mon, 19 Aug 2024 07:46:24 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id CFEBD1611B6 for ; Mon, 19 Aug 2024 11:46:23 +0000 (UTC) X-FDA: 82468817046.04.0B01601 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf16.hostedemail.com (Postfix) with ESMTP id 2BA7F18000A for ; Mon, 19 Aug 2024 11:46:21 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=none; spf=pass (imf16.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1724067904; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LPDMQZiK7kdOcRM0/7UbnSHMIQSuRYWqVU/2hj90wQ0=; b=Rr5QlfKo3PrS7H7J1snaNOR2jefm2F2h5XZGw1rfvmlB/bEqB9br3o3rc+Eg3Wzy1kOMmv sXkwSnNVUAPCb2CX+BRQJU/x5xJIwYSPuZ6UFcVpJ/icoJLiWrG5pApBH45y7WfQZ57HXu UfJekbt9nsO9JwchTvTacny2NEWInj8= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1724067904; a=rsa-sha256; cv=none; b=NRKTF7u6iY+4lkxA7VDWvy9P7YoYjpUw4Eb8hg91WY+aYrkrhV5BsrhIGwb6tqNaYZ2yOE C8XlZyixIw9GSmBVTOcw+m8tesBtLJuF3S/OYnMHy9nvCTcLq/Rm1kJMgKi4KnubaRZVQ8 EVN3WEzl2AfMrm/uvnb2l+Qj8Q4K6tM= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=none; spf=pass (imf16.hostedemail.com: domain of cmarinas@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=cmarinas@kernel.org; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=arm.com (policy=none) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 0420660B9C; Mon, 19 Aug 2024 11:46:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2DF1DC32782; Mon, 19 Aug 2024 11:46:15 +0000 (UTC) Date: Mon, 19 Aug 2024 12:46:13 +0100 From: Catalin Marinas To: Mark Brown Cc: Will Deacon , Jonathan Corbet , Andrew Morton , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Arnd Bergmann , Oleg Nesterov , Eric Biederman , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy , Kees Cook , "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , Thiago Jung Bauermann , Ross Burton , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v10 19/40] arm64/gcs: Context switch GCS state for EL0 Message-ID: References: <20240801-arm64-gcs-v10-0-699e2bd2190b@kernel.org> <20240801-arm64-gcs-v10-19-699e2bd2190b@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240801-arm64-gcs-v10-19-699e2bd2190b@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2BA7F18000A X-Stat-Signature: cua1atqyffjnf61a9hwyo7k8nujjpiu4 X-HE-Tag: 1724067981-663559 X-HE-Meta: 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 f1AGTLg2 70YKu9qniNzhnwh7EiUH70o7WkOVhWuHV65IXn4NkDRz7xsN1a+n23Xv4rwSB1C8CCu8vRQ/nH/GdknhnOfC2Ct8+e31Ifuon0tLOY+/7rKKdTaxWYTeTU6qJHj+6qHNYRRpp7kzigdlUBUEdppIWQ3QmXXTdIfM8LJJ1Crz/n+EVlM6bWw/HzdUc3hgA0T6PgmCKaSCatcMQ4ZoV6qAIBQKphwZqguiIcT3R0/15P20yk+iCDnTkkHYEs9MspOKTKn9HMOoCBQ2oBuHVAuazbzHtJhhL2WgCsWA1DzkVMYInl1JfAzAhmKP3/r9f4UvIjuZT/38bGt6EemSZNoMjFHgwxWIc7mXn2pF2zsRMBAMnvRU9T6ieB7zJj2kXmTZKOCEZX2wUGMA1TPnapHxjFeaas9LrE8uMHtknBaq4aIE0XmQ= 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: List-Subscribe: List-Unsubscribe: On Thu, Aug 01, 2024 at 01:06:46PM +0100, Mark Brown wrote: > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index 4ae31b7af6c3..5f00cb0da9c3 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c [...] > +static void gcs_thread_switch(struct task_struct *next) > +{ > + if (!system_supports_gcs()) > + return; > + > + gcs_preserve_current_state(); > + > + gcs_set_el0_mode(next); > + write_sysreg_s(next->thread.gcspr_el0, SYS_GCSPR_EL0); > + > + /* > + * Ensure that GCS changes are observable by/from other PEs in > + * case of migration. > + */ > + if (task_gcs_el0_enabled(current) || task_gcs_el0_enabled(next)) > + gcsb_dsync(); Could we do the sysreg writing under this 'if' block? If no app is using GCS (which would be the case for a while), it looks like unnecessary sysreg accesses. What's the GCSB DSYNC supposed to do here? The Arm ARM talks about ordering between GCS memory effects and other memory effects. I haven't looked at the memory model in detail yet (D11.9.1) but AFAICT it has nothing to do with the system registers. We'll need this barrier when ordering is needed between explicit or implicit (e.g. BL) GCS accesses and the explicit classic memory accesses. Paging comes to mind, so maybe flush_dcache_page() would need this barrier. ptrace() is another case if the memory accessed is a GCS page. I can see you added it in other places, I'll have a look as I go through the rest. But I don't think one is needed here. -- Catalin