From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: kvm PCI assignment & VFIO ramblings Date: Fri, 05 Aug 2011 20:26:11 +1000 Message-ID: <1312539971.8598.29.camel@pasglop> References: <1311983933.8793.42.camel@pasglop> <4E356221.6010302@redhat.com> <1312230476.2653.395.camel@bling.home> <20110804104105.GC22329@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Alex Williamson , Avi Kivity , kvm@vger.kernel.org, Anthony Liguori , David Gibson , Paul Mackerras , Alexey Kardashevskiy , "linux-pci@vger.kernel.org" , linuxppc-dev To: Joerg Roedel Return-path: In-Reply-To: <20110804104105.GC22329@8bytes.org> Sender: linux-pci-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, 2011-08-04 at 12:41 +0200, Joerg Roedel wrote: > On Mon, Aug 01, 2011 at 02:27:36PM -0600, Alex Williamson wrote: > > It's not clear to me how we could skip it. With VT-d, we'd have to > > implement an emulated interrupt remapper and hope that the guest picks > > unused indexes in the host interrupt remapping table before it could do > > anything useful with direct access to the MSI-X table. Maybe AMD IOMMU > > makes this easier? > > AMD IOMMU provides remapping tables per-device, and not a global one. > But that does not make direct guest-access to the MSI-X table safe. The > table contains the table contains the interrupt-type and the vector > which is used as an index into the remapping table by the IOMMU. So when > the guest writes into its MSI-X table the remapping-table in the host > needs to be updated too. Right, you need paravirt to avoid filtering :-) IE the problem is two fold: - Getting the right value in the table / remapper so things work (paravirt) - Protecting against the guest somewhat managing to change the value in the table (either directly or via a backdoor access to its own config space). The later for us comes from the HW PE filtering of the MSI transactions. Cheers, Ben.