From mboxrd@z Thu Jan 1 00:00:00 1970 From: Razvan Cojocaru Subject: Re: [PATCH V2] mem_event: Allow emulating an instruction that caused a page fault Date: Tue, 22 Jan 2013 14:53:49 +0200 Message-ID: <50FE8BDD.9080504@gmail.com> References: <50FDCBA8.1060000@gmail.com> <20130122123149.GA86613@ocelot.phlegethon.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130122123149.GA86613@ocelot.phlegethon.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Tim Deegan Cc: Andres Lagar-Cavilla , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org > #DF (-1, +12 = 55). Now that's a pretty unlikely scenario (and I may > have got some of the details wrong) but the upshot is: a single x86 > instruction can access enormous amounts of memory, so turning off > protection and single-stepping, especially if you don't trust the OS, is > exposing a lot more than the single frame you took the first fault on. Thank you, Tim, for clearing that up. Now, 'touching' a page is quite different from 'writing to' a page, and I'm really only interested in the latter. So, in a scenario where reads are permitted by default and we're only interested in writes, are we still talking about these limitations? A MOVSW, for example, only needs to write to a single page, even though it does touch more pages in read mode. Thanks, Razvan Cojocaru