From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zachary Amsden Subject: Re: pv_ops smp support Date: Thu, 19 Oct 2006 21:48:27 -0700 Message-ID: <4538551B.9080009@vmware.com> References: <453805BF.80301@goop.org> <45380B6A.3030104@vmware.com> <45380EDD.2070809@goop.org> <4538121E.7090607@vmware.com> <45384BAA.5070303@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <45384BAA.5070303@goop.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.osdl.org Errors-To: virtualization-bounces@lists.osdl.org To: Jeremy Fitzhardinge Cc: Chris Wright , Virtualization Mailing List List-Id: virtualization@lists.linuxfoundation.org Jeremy Fitzhardinge wrote: > >> I think you might want to optimize this a bit more, however, since in = >> some cases you will issue implicit shootdown IPIs during a pte update = >> hypercall. > > Not that I've seen, at least none that doesn't also exist in baseline. But if Xen uses direct page tables, the update to a page table through a = hypercall can cause other CPUs with that direct page table loaded to = require an invalidation. . Never mind, I see that you don't = require an immediate invalidation. Instead, you use page type = enforcement to guarantee that page remappings can not be used to subvert = hypervisor protection, and would either disallow or issue TLB = invalidations on page type changes from PT to writable pages. In that = case, the guest must use TLB shootdown to guarantee correctness, but no = extra TLB shootdowns are required to guarantee hypervisor security, as I = had feared. > >> This seems much cleaner than designing the shootdown semantic = >> directly into such PTE updates, which is I believe what some of the = >> older Xen patches did, although I could have misread them. > > I was starting on SMP with the idea that it would be relatively = > isolated and simple, but it seems I should probably do the MMU stuff = > first to see what impact it has on SMP. I think I was imagining some complications which really don't exist, but = it certainly doesn't hurt to consider the Xen MMU interfaces as you iron = out the SMP issues. So perhaps SMP will be more straightforward than I expected. Zach