From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40l3z40lS5zF35f for ; Tue, 15 May 2018 01:10:07 +1000 (AEST) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w4EF6dT7060621 for ; Mon, 14 May 2018 11:10:04 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 2hy9qbhab9-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 14 May 2018 11:10:04 -0400 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 14 May 2018 16:10:00 +0100 Subject: Re: [PATCH v10 06/25] mm: make pte_unmap_same compatible with SPF To: vinayak menon Cc: Andrew Morton , Michal Hocko , Peter Zijlstra , kirill@shutemov.name, ak@linux.intel.com, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com, Daniel Jordan , David Rientjes , Jerome Glisse , Ganesh Mahendran , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Paul McKenney , Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org, Vinayak Menon References: <1523975611-15978-1-git-send-email-ldufour@linux.vnet.ibm.com> <1523975611-15978-7-git-send-email-ldufour@linux.vnet.ibm.com> From: Laurent Dufour Date: Mon, 14 May 2018 17:09:48 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Message-Id: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 10/05/2018 18:15, vinayak menon wrote: > On Tue, Apr 17, 2018 at 8:03 PM, Laurent Dufour > wrote: >> pte_unmap_same() is making the assumption that the page table are still >> around because the mmap_sem is held. >> This is no more the case when running a speculative page fault and >> additional check must be made to ensure that the final page table are still >> there. >> >> This is now done by calling pte_spinlock() to check for the VMA's >> consistency while locking for the page tables. >> >> This is requiring passing a vm_fault structure to pte_unmap_same() which is >> containing all the needed parameters. >> >> As pte_spinlock() may fail in the case of a speculative page fault, if the >> VMA has been touched in our back, pte_unmap_same() should now return 3 >> cases : >> 1. pte are the same (0) >> 2. pte are different (VM_FAULT_PTNOTSAME) >> 3. a VMA's changes has been detected (VM_FAULT_RETRY) >> >> The case 2 is handled by the introduction of a new VM_FAULT flag named >> VM_FAULT_PTNOTSAME which is then trapped in cow_user_page(). >> If VM_FAULT_RETRY is returned, it is passed up to the callers to retry the >> page fault while holding the mmap_sem. >> >> Acked-by: David Rientjes >> Signed-off-by: Laurent Dufour >> --- >> include/linux/mm.h | 1 + >> mm/memory.c | 39 ++++++++++++++++++++++++++++----------- >> 2 files changed, 29 insertions(+), 11 deletions(-) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 4d1aff80669c..714da99d77a3 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -1208,6 +1208,7 @@ static inline void clear_page_pfmemalloc(struct page *page) >> #define VM_FAULT_NEEDDSYNC 0x2000 /* ->fault did not modify page tables >> * and needs fsync() to complete (for >> * synchronous page faults in DAX) */ >> +#define VM_FAULT_PTNOTSAME 0x4000 /* Page table entries have changed */ > > > This has to be added to VM_FAULT_RESULT_TRACE ? Indeed there is no chance that the macro VM_FAULT_RESULT_TRACE would have to translate that code to a string since VM_FAULT_PTNOTSAME is currently only returned by pte_unmap_same() and then converted by its only caller do_swap_page() to return 0. So VM_FAULT_PTNOTSAME is not expected to be seen outside of these services which are never using VM_FAULT_RESULT_TRACE(). This being said, this may be a good idea to add it in the case of future potential usage.