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=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 D195DC432BE for ; Thu, 2 Sep 2021 12:45:46 +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 93B36610E6 for ; Thu, 2 Sep 2021 12:45:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 93B36610E6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: List-Subscribe:List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id: In-Reply-To:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Reply-To:Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date :Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=zFyTa0OS+l5FAzfWBenYXPTGXu4W5DesDY3GXyuPhzg=; b=Ww1E+ykgXA4aKu5DWTMi0/QKZB 8uGZIcScnYdPQShGDV6x4q4mAXaGIYaUvG7GN/LOkVwaWiVeHfrgObHr+fFY4/TW9hOJsd81DKoXP e4kzzz9fLtN1sWLGUIPYecMd6lCcn+yaE1Zc43Iw+LqaixjA5cXtGfn5Na7Tno5j/zpovNhgFNQQG LJupaXb79GmWhSbqQUHJKIlsDaiFRAImSOoI6lZrFhk42t3NYK8lNBqJv6YuhggrNYyRrhxmjRhYJ WLVohxp3LlbTjoAxKJhjn5x+LaH6rwbyCRVQY5lIz1Y0S3ErupVZUXeF6K25A9d+sdeEdgTxDmBsb mAiIP1/A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mLm3k-009bUD-O5; Thu, 02 Sep 2021 12:43:12 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mLm3h-009bTp-3X for linux-arm-kernel@lists.infradead.org; Thu, 02 Sep 2021 12:43:10 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 524B8610CD; Thu, 2 Sep 2021 12:43:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1630586588; bh=Wxo1axyC1RgltZOdWyOqGv0mRYbku83X87olKpf4twE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ZzHfueiBNRMhcdxU5MRoXT6grmG2r7VxW7j27A1RRZED15GVu4SRZPswunUJHfZqc eBPIa7fEW8sT4BUyOc6Dbb8xbEAwc71a/McQLOY2y6TSJGQXbOGshOKUN4nVgvIZFX fX0IbIasm9Ae9qIZpCYj91Fg/Pf2QG8WRkZpjpJl5kEhP/zGigTHm2idt6urAWXFIY osnBdcwF+fJag+I8sn4cZAZbf2/juHUfQlMLZ0IDu5YyZIxYHvsAZwJ8qnpFtoTJr4 sdjkgSFHiiN5DbFDDcKhjl/pSmtVZcek/xbhAM8Wz0b3J9w3gLyfiHWM9j/0wEGQX5 8fTfkxZKUiROA== Date: Thu, 2 Sep 2021 13:42:36 +0100 From: Mark Brown To: Benjamin Herrenschmidt Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , benh@amazon.com, Szabolcs Nagy Subject: Re: ucontext, kernel vs. userspace (glibc) Message-ID: <20210902124236.GA4402@sirena.org.uk> References: <131d684ea46de6330ab90532ab73729d6c0690bd.camel@kernel.crashing.org> MIME-Version: 1.0 In-Reply-To: <131d684ea46de6330ab90532ab73729d6c0690bd.camel@kernel.crashing.org> X-Cookie: Better dead than mellow. User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210902_054309_210898_68EB57AD X-CRM114-Status: GOOD ( 20.83 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: multipart/mixed; boundary="===============5257040625873542435==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============5257040625873542435== Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="/04w6evG8XlLl3ft" Content-Disposition: inline --/04w6evG8XlLl3ft Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Mon, Aug 30, 2021 at 08:40:03PM +1000, Benjamin Herrenschmidt wrote: > So I'm discovering arm64 intricacies and today, as I was looking at SVE > support (in the context of distro glibc backports.. don't ask), I > noticed that glibc has no provision for dealing with kernel generated > ucontext's in its {get,set,swap}_context functions... > (It says so explicitly in the code unless I misunderstood). > So one thing we did to "solve" this on ppc64 a while ago was to create > a swapcontext syscall which can operate as all 3 operations (you can > have NULL arguments), which also handles the sigprocmask (bonus: > atomically with the context get/set from a userspace perspective). > Would it make sense to do something similar on aarch64 ? (And have > glibc then exploit it). I think the usefulness of such an interface is mainly a question for userspace - I don't immediately see any issue with implementing it if it's useful to people. > The hard-to-solve thing is the case where the SVE context spills > outside of the ucontext itself, in the extra room on the stack, since > programs that "now" about ucontext will not have allocated space for > that, so that's more/less a lost cause already. You can figure out the maximum possible size for a context so it would be possible to define a mechanism for pointing to extra data I guess but yeah, it's going to be a problem when we start seeing systems with large enough register state. --/04w6evG8XlLl3ft Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmEwxrwACgkQJNaLcl1U h9AaLwf9GFQWfww8WU74/JZZdrxeQ8mnZiY2OrFrmSoGepDXgiq0u9QjGsEEGbjJ CoVecP9FtusdZNWfg+RPdXtk8N0G6cyAE4Mrqaz+0RFw+9tTZ3PsdbK4fqolruyK Q3E4GIC49XEn3lfohh7qM9s56LMY+dKJJu+MnGw6foZSEvr47LQsFtn42TfvSeup Wk3w4zEE8lyrR593KfpdCoGHuPc17YRKAGi+QvsxmyGXpa5InSQZVFFvMcUCLffF CyQ3Y3THTt/rjf5ttMxZ46Ui4mA5EM3gODg/lrEx7fmfX45lJTLENJ6ZKAm9hk01 gMjUhQ8qfzaKkx7NsH819rx9EMu0HQ== =qYNF -----END PGP SIGNATURE----- --/04w6evG8XlLl3ft-- --===============5257040625873542435== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============5257040625873542435==--