From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Masters Subject: Re: [RFC PATCH 0/2] Missing READ_ONCE in core and arch-specific pgtable code leading to crashes Date: Thu, 28 Sep 2017 15:38:00 -0400 Message-ID: <9f351432-3c6b-3b06-7b49-bc9a5806aff5@redhat.com> References: <1506527369-19535-1-git-send-email-will.deacon@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1506527369-19535-1-git-send-email-will.deacon@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Will Deacon , peterz@infradead.org, paulmck@linux.vnet.ibm.com, kirill.shutemov@linux.intel.com Cc: linux-kernel@vger.kernel.org, ynorov@caviumnetworks.com, rruigrok@codeaurora.org, linux-arch@vger.kernel.org, akpm@linux-foundation.org, catalin.marinas@arm.com List-Id: linux-arch.vger.kernel.org On 09/27/2017 11:49 AM, Will Deacon wrote: > The moral of the story is that read-after-read (same address) ordering *only* > applies if READ_ONCE is used consistently. This means we need to fix page > table dereferences in the core code as well as the arch code to avoid this > problem. The two RFC patches in this series fix arm64 (which is a bigger fix > that necessary since I clean things up too) and page_vma_mapped_walk. > > Comments welcome. Thanks for this Will. I'll echo Timur's comment that it would be ideal to split this up into the critical piece needed for ordering access/update to the PMD in the face of a THP split and separately have the cosmetic cleanups. Needless to say, we've got a bunch of people who are tracking this one and tracking it ready for backport. We just got THP re-enabled so I'm pretty keen that we not have to disable again. Jon. -- Computer Architect | Sent from my Fedora powered laptop From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:51204 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750759AbdI1TiH (ORCPT ); Thu, 28 Sep 2017 15:38:07 -0400 Subject: Re: [RFC PATCH 0/2] Missing READ_ONCE in core and arch-specific pgtable code leading to crashes References: <1506527369-19535-1-git-send-email-will.deacon@arm.com> From: Jon Masters Message-ID: <9f351432-3c6b-3b06-7b49-bc9a5806aff5@redhat.com> Date: Thu, 28 Sep 2017 15:38:00 -0400 MIME-Version: 1.0 In-Reply-To: <1506527369-19535-1-git-send-email-will.deacon@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Will Deacon , peterz@infradead.org, paulmck@linux.vnet.ibm.com, kirill.shutemov@linux.intel.com Cc: linux-kernel@vger.kernel.org, ynorov@caviumnetworks.com, rruigrok@codeaurora.org, linux-arch@vger.kernel.org, akpm@linux-foundation.org, catalin.marinas@arm.com Message-ID: <20170928193800.NxkNZx94sRpBZYDONaHmDLZYMBjRYzZlhzSGLb8fPuI@z> On 09/27/2017 11:49 AM, Will Deacon wrote: > The moral of the story is that read-after-read (same address) ordering *only* > applies if READ_ONCE is used consistently. This means we need to fix page > table dereferences in the core code as well as the arch code to avoid this > problem. The two RFC patches in this series fix arm64 (which is a bigger fix > that necessary since I clean things up too) and page_vma_mapped_walk. > > Comments welcome. Thanks for this Will. I'll echo Timur's comment that it would be ideal to split this up into the critical piece needed for ordering access/update to the PMD in the face of a THP split and separately have the cosmetic cleanups. Needless to say, we've got a bunch of people who are tracking this one and tracking it ready for backport. We just got THP re-enabled so I'm pretty keen that we not have to disable again. Jon. -- Computer Architect | Sent from my Fedora powered laptop