On Fri, Aug 05, 2011 at 08:26:11PM +1000, Benjamin Herrenschmidt wrote: > 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 :-) Or a shadow MSI-X table like done on x86. How to handle this seems to be platform specific. As you indicate there is a standardized paravirt interface for that on Power. > 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. Right. The second part of the problem can be avoided with interrupt-remapping/filtering hardware in the IOMMUs. Joerg -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
