From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:4034 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2409541AbgDPO7N (ORCPT ); Thu, 16 Apr 2020 10:59:13 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 03GErAxg118360 for ; Thu, 16 Apr 2020 10:59:12 -0400 Received: from e06smtp04.uk.ibm.com (e06smtp04.uk.ibm.com [195.75.94.100]) by mx0a-001b2d01.pphosted.com with ESMTP id 30esh4042s-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 16 Apr 2020 10:59:12 -0400 Received: from localhost by e06smtp04.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 16 Apr 2020 15:58:31 +0100 Date: Thu, 16 Apr 2020 16:59:00 +0200 From: Claudio Imbrenda Subject: Re: [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible pages In-Reply-To: References: <20200306132537.783769-1-imbrenda@linux.ibm.com> <20200306132537.783769-3-imbrenda@linux.ibm.com> <3ae46945-0c7b-03cd-700a-a6fe8003c6ab@intel.com> <20200415221754.GM2483@worktop.programming.kicks-ass.net> <20200416141547.29be5ea0@p-imbrenda> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20200416165900.68bd4dba@p-imbrenda> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Dave Hansen Cc: Peter Zijlstra , Andy Lutomirski , linux-next@vger.kernel.org, akpm@linux-foundation.org, jack@suse.cz, kirill@shutemov.name, "Edgecombe, Rick P" , Sean Christopherson , borntraeger@de.ibm.com, david@redhat.com, aarcange@redhat.com, linux-mm@kvack.org, frankja@linux.ibm.com, sfr@canb.auug.org.au, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Will Deacon , "Williams, Dan J" On Thu, 16 Apr 2020 07:20:48 -0700 Dave Hansen wrote: > On 4/16/20 5:15 AM, Claudio Imbrenda wrote: > >> I assumed that this was all anonymous-only so it's always dirty > >> before writeback starts. > > it could also be mmapped > > Let's say you have a mmap()'d ramfs file. Another process calls which > doesn't have it mapped calls sys_write() and writes to the file. > > This means that host host has to write to the physical page and must > do arch_make_page_accessible() in the sys_write() path somewhere. > > There is a get_user_pages() in that path, but it's on the _source_ > buffer, not the ramfs page because the ramfs page is not mapped. > There's also no __test_set_page_writeback() because you can't write > back ramfs. > > Where is the arch_make_page_accessible() in this case on the ramfs > page? it's in the fault handler for the exception the CPU will get when attempting to write the data to the protected page