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 15:47:34 +0200 Message-ID: <50FE9876.8030907@gmail.com> References: <50FDCBA8.1060000@gmail.com> <20130122123149.GA86613@ocelot.phlegethon.org> <50FE8BDD.9080504@gmail.com> <20130122132059.GA87324@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: <20130122132059.GA87324@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 > Ok, talking only about writes, we have the destination operand, plus all > the pagetables (for setting Accessed bits) plus any stacks and TSSes > needed in delivering faults; something like 32 pages for the full > double-fault scenario. I see, but then, even setting aside Andres' argument that having all possible events sent to userspace is far from trivial, doing so would completely cripple the monitored domain speed-wise. Imagine having userspace having to decide if it allows a write 32 times per one instruction. Even with its limitations, this patch at least gives us a shot at looking at what the domain does with memory - the existing model (releasing the page completely to allow the write) is not fit for anything like this at all. So far, between the requirements of reasonable demands on the domU, and satisfactory levels of control provided by the received mem_events, at least as far as writes go, the patch's done it's job quite nicely. Thanks, Razvan Cojocaru