From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: kvm PCI assignment & VFIO ramblings Date: Fri, 5 Aug 2011 14:57:09 +0200 Message-ID: <20110805125709.GB30353@8bytes.org> References: <1311983933.8793.42.camel@pasglop> <4E356221.6010302@redhat.com> <1312230476.2653.395.camel@bling.home> <20110804104105.GC22329@8bytes.org> <1312539971.8598.29.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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: Benjamin Herrenschmidt Return-path: Content-Disposition: inline In-Reply-To: <1312539971.8598.29.camel@pasglop> Sender: linux-pci-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from 8bytes.org (8bytes.org [88.198.83.132]) by ozlabs.org (Postfix) with ESMTP id 9AC9FB6F6F for ; Fri, 5 Aug 2011 22:57:14 +1000 (EST) Date: Fri, 5 Aug 2011 14:57:09 +0200 From: Joerg Roedel To: Benjamin Herrenschmidt Subject: Re: kvm PCI assignment & VFIO ramblings Message-ID: <20110805125709.GB30353@8bytes.org> References: <1311983933.8793.42.camel@pasglop> <4E356221.6010302@redhat.com> <1312230476.2653.395.camel@bling.home> <20110804104105.GC22329@8bytes.org> <1312539971.8598.29.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1312539971.8598.29.camel@pasglop> Cc: Alexey Kardashevskiy , kvm@vger.kernel.org, Paul Mackerras , "linux-pci@vger.kernel.org" , David Gibson , Alex Williamson , Avi Kivity , Anthony Liguori , linuxppc-dev List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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