From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [PATCH] VMI: remove CONFIG_DEBUG_PAGE_TYPE and associated bitrotted code Date: Fri, 06 Jul 2007 14:01:45 -0700 Message-ID: <468EADB9.9050802@goop.org> References: <468E890A.1070504@s5r6.in-berlin.de> <20070706201625.GT4306@sequoia.sous-sol.org> <468EA27C.9060401@vmware.com> <468EA5E0.4070501@goop.org> <468EA74D.7010706@vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <468EA74D.7010706@vmware.com> Sender: linux-kernel-owner@vger.kernel.org To: Zachary Amsden Cc: Chris Wright , Linux Kernel Mailing List , virtualization@lists.osdl.org, Stefan Richter , "Robert P. J. Day" , Rusty Russell , Martin Schwidefsky , Carsten Otte , Andrew Morton List-Id: virtualization@lists.linuxfoundation.org Zachary Amsden wrote: > I though about it, but it gets really ugly. You need wrappers for all > the MMU ops in pvops generic code, which means either another layer of > wrappers or a bunch of CONFIG_DEBUG_PARAVIRT Oh, yes, more wrappers please! We could do it at the paravirt_ops level: set up your pv_ops, then call paravirt_debug_mmuops(), which would save away your ops and replace them with wrappers. That basic structure would lend itself to all kinds of paravirt-level debugging tools. It would be a bit more elegant if we had mmu_ops. Maybe we should do that splitup before 64bit? > only things that are easy to break because they also depend on PAE vs. > non-PAE. Hm, would they? Would they need to inspect the content of the pte_t (etc), or just look at the struct page for the page being updated? (pmd operations being a bit more awkward, of course.) > It's doable, though, and might even be extensible to s390 for CMM page > type debugging, as well as descriptor type tracking and enforcement of > page isolation of GDTs. > > Page state tracking could track - > > PAGE_ZERO, PAGE_UNUSED, PAGE_STABLE, PAGE_VOLATILE, > PAGE_POTENTIALLY_VOLATILE, PAGE_L1{2/3/4}, PAGE_LDT, PAGE_GDT, > > actually, no this seems silly, since we'd just be duplicating bits for > the page types, so the only debug benefit is ensuring the intersection > of volatile and L{1/2/3/4} is nil, which is already trivially > verifiable by inspection. Well, I have to say that keeping the hypervisor hints in sync with the actual kernel-level page state worries me, so any debug tools which could help there would be good. This seems like it should be the right place to do it, but I can't say I've thought about it in any detail. Of course, if it *is* helpful to the page hinting patches, then it suggests that it's a facility with wider scope than pv-ops. J