From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vk0-f69.google.com (mail-vk0-f69.google.com [209.85.213.69]) by kanga.kvack.org (Postfix) with ESMTP id B00D36B0005 for ; Mon, 2 May 2016 13:24:08 -0400 (EDT) Received: by mail-vk0-f69.google.com with SMTP id s68so5223103vkg.1 for ; Mon, 02 May 2016 10:24:08 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id j44si5326888qgd.86.2016.05.02.10.24.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 May 2016 10:24:08 -0700 (PDT) Date: Mon, 2 May 2016 18:22:11 +0200 From: Oleg Nesterov Subject: Re: GUP guarantees wrt to userspace mappings redesign Message-ID: <20160502162211.GA11678@redhat.com> References: <20160428232127.GL11700@redhat.com> <20160429005106.GB2847@node.shutemov.name> <20160428204542.5f2053f7@ul30vt.home> <20160429070611.GA4990@node.shutemov.name> <20160429163444.GM11700@redhat.com> <20160502104119.GA23305@node.shutemov.name> <20160502111513.GA4079@gmail.com> <20160502121402.GB23305@node.shutemov.name> <20160502141538.GA5961@redhat.com> <20160502162128.GF24419@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160502162128.GF24419@node.shutemov.name> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Jerome Glisse , Hugh Dickins , Linus Torvalds , Andrew Morton , Andrea Arcangeli , Alex Williamson , kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, "linux-mm@kvack.org" On 05/02, Kirill A. Shutemov wrote: > > On Mon, May 02, 2016 at 04:15:38PM +0200, Oleg Nesterov wrote: > > > > > > - I don't see any check page_count() around __replace_page() in uprobes, > > > so it can easily replace pinned page. > > > > Why it should? even if it races with get_user_pages_fast()... this doesn't > > differ from the case when an application writes to MAP_PRIVATE non-anonymous > > region, no? > > < I know nothing about uprobes or ptrace in general > > > I think the difference is that the write is initiated by the process > itself, but IIUC __replace_page() can be initiated by other process, so > it's out of control of the application. Yes. Just like gdb can insert a breakpoint into the read-only executable vma. > So we have pages pinned by a driver and the driver expects the pinned > pages to be mapped into userspace, then __replace_page() kicks in and put > different page there -- driver's expectation is broken. Yes... but I don't understand the problem space. I mean, I do not know why this driver should expect this, how it can be broken, etc. I do not even understand why "initiated by other process" can make any difference... Unless this driver somehow controls all threads which could have this page mapped. Oleg. -- 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