From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f42.google.com (mail-wm0-f42.google.com [74.125.82.42]) by kanga.kvack.org (Postfix) with ESMTP id 709256B0253 for ; Thu, 19 Nov 2015 05:50:38 -0500 (EST) Received: by wmec201 with SMTP id c201so19085156wme.0 for ; Thu, 19 Nov 2015 02:50:37 -0800 (PST) Received: from e06smtp15.uk.ibm.com (e06smtp15.uk.ibm.com. [195.75.94.111]) by mx.google.com with ESMTPS id m12si11283460wmg.108.2015.11.19.02.50.36 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 19 Nov 2015 02:50:37 -0800 (PST) Received: from localhost by e06smtp15.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 19 Nov 2015 10:50:36 -0000 Received: from b06cxnps4074.portsmouth.uk.ibm.com (d06relay11.portsmouth.uk.ibm.com [9.149.109.196]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id CCF4917D805F for ; Thu, 19 Nov 2015 10:50:53 +0000 (GMT) Received: from d06av01.portsmouth.uk.ibm.com (d06av01.portsmouth.uk.ibm.com [9.149.37.212]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id tAJAoVfC2556320 for ; Thu, 19 Nov 2015 10:50:31 GMT Received: from d06av01.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av01.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id tAJAoU0g029951 for ; Thu, 19 Nov 2015 03:50:31 -0700 Date: Thu, 19 Nov 2015 11:50:27 +0100 From: Dominik Dingel Subject: Re: [PATCH 2/2] s390/mm: allow gmap code to retry on faulting in guest memory Message-ID: <20151119115027.620143d4@BR9TG4T3.de.ibm.com> In-Reply-To: <564D8774.8090206@de.ibm.com> References: <1447890598-56860-1-git-send-email-dingel@linux.vnet.ibm.com> <1447890598-56860-3-git-send-email-dingel@linux.vnet.ibm.com> <20151119091808.5d84c8ba@mschwide> <564D8774.8090206@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christian Borntraeger Cc: Martin Schwidefsky , linux-s390@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , "Kirill A. Shutemov" , Andrea Arcangeli , David Rientjes , Eric B Munson , Naoya Horiguchi , Mel Gorman , Heiko Carstens , Paolo Bonzini , "Jason J. Herne" , linux-kernel@vger.kernel.org, "Kirill A. Shutemov" On Thu, 19 Nov 2015 09:25:24 +0100 Christian Borntraeger wrote: > On 11/19/2015 09:18 AM, Martin Schwidefsky wrote: > > On Thu, 19 Nov 2015 00:49:58 +0100 > > Dominik Dingel wrote: > > > >> The userfaultfd does need FAULT_FLAG_ALLOW_RETRY to not return > >> VM_FAULT_SIGBUS. So we improve the gmap code to handle one > >> VM_FAULT_RETRY. > >> > >> Signed-off-by: Dominik Dingel > >> --- > >> arch/s390/mm/pgtable.c | 28 ++++++++++++++++++++++++---- > >> 1 file changed, 24 insertions(+), 4 deletions(-) > >> > >> diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c > >> index 54ef3bc..8a0025d 100644 > >> --- a/arch/s390/mm/pgtable.c > >> +++ b/arch/s390/mm/pgtable.c > >> @@ -577,15 +577,22 @@ int gmap_fault(struct gmap *gmap, unsigned long gaddr, > >> unsigned int fault_flags) > >> { > >> unsigned long vmaddr; > >> - int rc; > >> + int rc, fault; > >> > >> + fault_flags |= FAULT_FLAG_ALLOW_RETRY; > >> +retry: > >> down_read(&gmap->mm->mmap_sem); > >> vmaddr = __gmap_translate(gmap, gaddr); > >> if (IS_ERR_VALUE(vmaddr)) { > >> rc = vmaddr; > >> goto out_up; > >> } > >> - if (fixup_user_fault(current, gmap->mm, vmaddr, fault_flags)) { > >> + fault = fixup_user_fault(current, gmap->mm, vmaddr, fault_flags); > >> + if (fault & VM_FAULT_RETRY) { > >> + fault_flags &= ~FAULT_FLAG_ALLOW_RETRY; > >> + fault_flags |= FAULT_FLAG_TRIED; > >> + goto retry; > >> + } else if (fault) { > >> rc = -EFAULT; > >> goto out_up; > >> } > > > > Me thinks that you want to add the retry code into fixup_user_fault itself. > > You basically have the same code around the three calls to fixup_user_fault. > > Yes, it will be a common code patch but I guess that it will be acceptable > > given userfaultfd as a reason. > > That makes a lot of sense. In an earlier discussion (a followup of Jasons > mm: Loosen MADV_NOHUGEPAGE to enable Qemu postcopy on s390) patch. > > Andrea suggested the following: > > It's probably better to add a fixup_user_fault_unlocked that will work > like get_user_pages_unlocked. I.e. leaves the details of the mmap_sem > locking internally to the function, and will handle VM_FAULT_RETRY > automatically by re-taking the mmap_sem and repeating the > fixup_user_fault after updating the FAULT_FLAG_ALLOW_RETRY to > FAULT_FLAG_TRIED. I know, I saw his mail. But within the gmap code we need to take the mmap_sem before calling fixup_user_fault as well as holding it for later on like __gmap_link. We could introduce a new wrapper arround fixup_user_fault, like: fixup_user_fault_retry, which would take care of the retry logic, but does not encapsulate the complete mmap_sem logic. @Kirill would that be acceptable for you as well? -- 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