From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f43.google.com (mail-wm0-f43.google.com [74.125.82.43]) by kanga.kvack.org (Postfix) with ESMTP id 7233E6B0253 for ; Thu, 19 Nov 2015 03:25:30 -0500 (EST) Received: by wmec201 with SMTP id c201so13225125wme.0 for ; Thu, 19 Nov 2015 00:25:30 -0800 (PST) Received: from e06smtp17.uk.ibm.com (e06smtp17.uk.ibm.com. [195.75.94.113]) by mx.google.com with ESMTPS id j4si1531868wje.220.2015.11.19.00.25.29 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 19 Nov 2015 00:25:29 -0800 (PST) Received: from localhost by e06smtp17.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 19 Nov 2015 08:25:28 -0000 Received: from b06cxnps3074.portsmouth.uk.ibm.com (d06relay09.portsmouth.uk.ibm.com [9.149.109.194]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id BC2FA1B0806B for ; Thu, 19 Nov 2015 08:25:46 +0000 (GMT) Received: from d06av09.portsmouth.uk.ibm.com (d06av09.portsmouth.uk.ibm.com [9.149.37.250]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id tAJ8PQtt8520166 for ; Thu, 19 Nov 2015 08:25:26 GMT Received: from d06av09.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av09.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id tAJ8PPBT010975 for ; Thu, 19 Nov 2015 01:25:26 -0700 Subject: Re: [PATCH 2/2] s390/mm: allow gmap code to retry on faulting in guest memory 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> From: Christian Borntraeger Message-ID: <564D8774.8090206@de.ibm.com> Date: Thu, 19 Nov 2015 09:25:24 +0100 MIME-Version: 1.0 In-Reply-To: <20151119091808.5d84c8ba@mschwide> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Martin Schwidefsky , Dominik Dingel Cc: 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 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. -- 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