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[209.85.220.65]) by mx.google.com with SMTPS id c15sor9875342pls.61.2019.06.12.04.14.42 for (Google Transport Security); Wed, 12 Jun 2019 04:14:42 -0700 (PDT) Received-SPF: pass (google.com: domain of andreyknvl@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=QkhZMvI8; spf=pass (google.com: domain of andreyknvl@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=andreyknvl@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ICAcqmNM80YqXGU9u0yKcUq/onm/SsQo2SDs/l3f+hY=; b=QkhZMvI8xgho9eMFZ7w6J/3duhWcdGLEkVVUAU2qSaxNfXU+GXLc+PdiUdCpUn61iY 0xCUxQ9wiA1Jj7ZnvEwSzmljdVe71a10tK0t/VIk6vJ6KuoIESh9plrNP00oJ9EUV9CE 7ZXKJL/NmCDrLh5D1fRV3U/5XcSqnaFIYrJ7IhnmnWDC1y2ZQhZMwMFDrVZ4wkPjj2PR KjnNxVxOeNHsZ1yb6hgnM2H6TbZTzWPz9Cffq6e0f9rEpBuiI2bynmdfsgpQFhae4y5r LLRsk0MnIrY8OwbkGOOGkhYBEu+P7mFEBBswTcH9Mhn9r0qq9AEF/SsRyiNTxER5NtY3 eTUQ== X-Google-Smtp-Source: APXvYqygEZ27HGfNqszCpdSgojAf7S6ru14/DaT8Or0Syv3FL9sWDfZ+9LXBU0/5Hxbzx8tkSmaHaZjTcL+f/jghf7s= X-Received: by 2002:a17:902:8609:: with SMTP id f9mr75570344plo.252.1560338081704; Wed, 12 Jun 2019 04:14:41 -0700 (PDT) MIME-Version: 1.0 References: <9e1b5998a28f82b16076fc85ab4f88af5381cf74.1559580831.git.andreyknvl@google.com> <20190611150122.GB63588@arrakis.emea.arm.com> <20190611175037.pflr6q6ob67zjj25@mbp> In-Reply-To: <20190611175037.pflr6q6ob67zjj25@mbp> From: Andrey Konovalov Date: Wed, 12 Jun 2019 13:14:30 +0200 Message-ID: Subject: Re: [PATCH v16 16/16] selftests, arm64: add a selftest for passing tagged pointers to kernel To: Catalin Marinas Cc: Linux ARM , Linux Memory Management List , LKML , amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, "open list:KERNEL SELFTEST FRAMEWORK" , Vincenzo Frascino , Will Deacon , Mark Rutland , Andrew Morton , Greg Kroah-Hartman , Kees Cook , Yishai Hadas , Felix Kuehling , Alexander Deucher , Christian Koenig , Mauro Carvalho Chehab , Jens Wiklander , Alex Williamson , Leon Romanovsky , Luc Van Oostenryck , Dave Martin , Khalid Aziz , enh , Jason Gunthorpe , Christoph Hellwig , Dmitry Vyukov , Kostya Serebryany , Evgeniy Stepanov , Lee Smith , Ramana Radhakrishnan , Jacob Bramley , Ruben Ayrapetyan , Robin Murphy , Kevin Brodsky , Szabolcs Nagy Content-Type: text/plain; charset="UTF-8" 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 Tue, Jun 11, 2019 at 7:50 PM Catalin Marinas wrote: > > On Tue, Jun 11, 2019 at 07:18:04PM +0200, Andrey Konovalov wrote: > > On Tue, Jun 11, 2019 at 5:01 PM Catalin Marinas wrote: > > > static void *tag_ptr(void *ptr) > > > { > > > static int tagged_addr_err = 1; > > > unsigned long tag = 0; > > > > > > if (tagged_addr_err == 1) > > > tagged_addr_err = prctl(PR_SET_TAGGED_ADDR_CTRL, > > > PR_TAGGED_ADDR_ENABLE, 0, 0, 0); > > > > I think this requires atomics. malloc() can be called from multiple threads. > > It's slightly racy but I assume in a real libc it can be initialised > earlier than the hook calls while still in single-threaded mode (I had > a quick attempt with __attribute__((constructor)) but didn't get far). > > Even with the race, under normal circumstances calling the prctl() twice > is not a problem. I think the risk here is that someone disables the ABI > via sysctl and the ABI is enabled for some of the threads only. OK, I'll keep the code racy, but add a comment pointing it out. Thanks! > > -- > Catalin