From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f69.google.com (mail-oi0-f69.google.com [209.85.218.69]) by kanga.kvack.org (Postfix) with ESMTP id 86C0B6B0280 for ; Wed, 22 Nov 2017 07:49:37 -0500 (EST) Received: by mail-oi0-f69.google.com with SMTP id e142so7537435oih.5 for ; Wed, 22 Nov 2017 04:49:37 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id o84si5952520oib.331.2017.11.22.04.49.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Nov 2017 04:49:36 -0800 (PST) Subject: Re: MPK: removing a pkey References: <0f006ef4-a7b5-c0cf-5f58-d0fd1f911a54@redhat.com> <8741e4d6-6ac0-9c07-99f3-95d8d04940b4@suse.cz> <813f9736-36dd-b2e5-c850-9f2d5f94514a@redhat.com> From: Florian Weimer Message-ID: <6299ccb2-ca6b-b49e-fca0-6baa0d6581a9@redhat.com> Date: Wed, 22 Nov 2017 13:49:33 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka , Dave Hansen , linux-x86_64@vger.kernel.org, linux-arch@vger.kernel.org Cc: linux-mm , Linux API On 11/22/2017 01:46 PM, Vlastimil Babka wrote: > On 11/22/2017 01:15 PM, Florian Weimer wrote: >> On 11/22/2017 09:18 AM, Vlastimil Babka wrote: >>> And, was the pkey == -1 internal wiring supposed to be exposed to the >>> pkey_mprotect() signal, or should there have been a pre-check returning >>> EINVAL in SYSCALL_DEFINE4(pkey_mprotect), before calling >>> do_mprotect_pkey())? I assume it's too late to change it now anyway (or >>> not?), so should we also document it? >> >> I think the -1 case to the set the default key is useful because it >> allows you to use a key value of -1 to mean a??MPK is not supporteda??, and >> still call pkey_mprotect. > > Hmm the current manpage says then when MPK is not supported, pkey has to > be specified 0. Which is a value that doesn't work when MPK *is* > supported. So -1 is more universal indeed. -1 also chosen a different key if key 0 does not support the requested protection flags. >> I plan to document this behavior on the glibc side, and glibc will call >> mprotect (not pkey_mprotect) for key -1, so that you won't get ENOSYS >> with kernels which do not support pkey_mprotect. > > Fair enough. What will you do about pkey_alloc() in that case, emulate > ENOSPC? Oh, the manpage already suggests so. And the return value in > that case is... -1. Makes sense :) The manual page is incorrect, the kernel actually returns EINVAL. Applications should check for EINVAL (and also ENOSYS) and activate fallback code. Using -1 directly would be a bit reckless IMHO. Thanks Florian -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org