From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754639AbdH2Oul (ORCPT ); Tue, 29 Aug 2017 10:50:41 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48523 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751386AbdH2Ouj (ORCPT ); Tue, 29 Aug 2017 10:50:39 -0400 Subject: Re: [PATCH v2 19/20] x86/mm: Add speculative pagefault handling To: Anshuman Khandual , 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 Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org References: <1503007519-26777-1-git-send-email-ldufour@linux.vnet.ibm.com> <1503007519-26777-20-git-send-email-ldufour@linux.vnet.ibm.com> From: Laurent Dufour Date: Tue, 29 Aug 2017 16:50:26 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: fr Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 17082914-0016-0000-0000-000004E7276F X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17082914-0017-0000-0000-000028209DBC Message-Id: <37b9b036-e951-0a74-3e5c-31049cda7dd2@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-29_04:,, 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-1708290223 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/08/2017 09:29, Anshuman Khandual wrote: > 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. Yes I think this is doable in the case of x86.