From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751746AbdHUHa5 (ORCPT ); Mon, 21 Aug 2017 03:30:57 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:53154 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751088AbdHUHa4 (ORCPT ); Mon, 21 Aug 2017 03:30:56 -0400 Subject: Re: [PATCH v2 19/20] x86/mm: Add speculative pagefault handling To: Laurent Dufour , paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, 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 References: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> <1503007519-26777-20-git-send-email-ldufour@linux.vnet.ibm.com> Cc: 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, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org From: Anshuman Khandual Date: Mon, 21 Aug 2017 12:59:24 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <1503007519-26777-20-git-send-email-ldufour@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17082107-0040-0000-0000-00000350D390 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17082107-0041-0000-0000-00000CCEA581 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-21_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1708210121 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/18/2017 03:35 AM, Laurent Dufour wrote: > From: Peter Zijlstra > > Try a speculative fault before acquiring mmap_sem, if it returns with > VM_FAULT_RETRY continue with the mmap_sem acquisition and do the > traditional fault. > > Signed-off-by: Peter Zijlstra (Intel) > > [Clearing of FAULT_FLAG_ALLOW_RETRY is now done in > handle_speculative_fault()] > [Retry with usual fault path in the case VM_ERROR is returned by > handle_speculative_fault(). This allows signal to be delivered] > Signed-off-by: Laurent Dufour > --- > arch/x86/include/asm/pgtable_types.h | 7 +++++++ > arch/x86/mm/fault.c | 19 +++++++++++++++++++ > 2 files changed, 26 insertions(+) > > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h > index bf9638e1ee42..4fd2693a037e 100644 > --- a/arch/x86/include/asm/pgtable_types.h > +++ b/arch/x86/include/asm/pgtable_types.h > @@ -234,6 +234,13 @@ enum page_cache_mode { > #define PGD_IDENT_ATTR 0x001 /* PRESENT (no other attributes) */ > #endif > > +/* > + * Advertise that we call the Speculative Page Fault handler. > + */ > +#ifdef CONFIG_X86_64 > +#define __HAVE_ARCH_CALL_SPF > +#endif > + > #ifdef CONFIG_X86_32 > # include > #else > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > index 2a1fa10c6a98..4c070b9a4362 100644 > --- a/arch/x86/mm/fault.c > +++ b/arch/x86/mm/fault.c > @@ -1365,6 +1365,24 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code, > if (error_code & PF_INSTR) > flags |= FAULT_FLAG_INSTRUCTION; > > +#ifdef __HAVE_ARCH_CALL_SPF > + if (error_code & PF_USER) { > + fault = handle_speculative_fault(mm, address, flags); > + > + /* > + * We also check against VM_FAULT_ERROR because we have to > + * raise a signal by calling later mm_fault_error() which > + * requires the vma pointer to be set. So in that case, > + * we fall through the normal path. Cant mm_fault_error() be called inside handle_speculative_fault() ? Falling through the normal page fault path again just to raise a signal seems overkill. Looking into mm_fault_error(), it seems they are different for x86 and powerpc. X86: mm_fault_error(struct pt_regs *regs, unsigned long error_code, unsigned long address, struct vm_area_struct *vma, unsigned int fault) powerpc: mm_fault_error(struct pt_regs *regs, unsigned long addr, int fault) Even in case of X86, I guess we would have reference to the faulting VMA (after the SRCU search) which can be used to call this function directly.