From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [PATCH 00/10] KVM PCIe/MSI passthrough on ARM/ARM64 Date: Wed, 3 Feb 2016 16:36:06 +0100 Message-ID: <20160203153606.GC13974@cbox> References: <1453813968-2024-1-git-send-email-eric.auger@linaro.org> <1454017899.23148.0.camel@redhat.com> <56AB78B1.2030202@linaro.org> <1454096004.9301.1.camel@redhat.com> <56ABD8E0.6080409@linaro.org> <20160201140351.GE6828@arm.com> <20160203125047.GB13974@cbox> <20160203131057.GA20217@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20160203131057.GA20217-5wv7dgnIgG8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Will Deacon Cc: eric.auger-qxv4g6HH51o@public.gmane.org, kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Eric Auger , marc.zyngier-5wv7dgnIgG8@public.gmane.org, patches-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, p.fedin-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, pranav.sawargaonkar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, kvmarm-FPEHb7Xf0XXUo1n7N8X6UoWGPAHP3yOg@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: iommu@lists.linux-foundation.org On Wed, Feb 03, 2016 at 01:10:58PM +0000, Will Deacon wrote: > On Wed, Feb 03, 2016 at 01:50:47PM +0100, Christoffer Dall wrote: > > On Mon, Feb 01, 2016 at 02:03:51PM +0000, Will Deacon wrote: > > > On Fri, Jan 29, 2016 at 10:25:52PM +0100, Eric Auger wrote: > > > > On 01/29/2016 08:33 PM, Alex Williamson wrote: > > > > >>> We know that x86 handles MSI vectors specially, so there is some > > > > >>> hardware that helps the situation. It's not just that x86 has a fixed > > > > >>> range for MSI, it's how it manages that range when interrupt remapping > > > > >>> hardware is enabled. A device table indexed by source-ID references a > > > > >>> per device table indexed by data from the MSI write itself. So we get > > > > >>> much, much finer granularity, > > > > >> About the granularity, I think ARM GICv3 now provides a similar > > > > >> capability with GICv3 ITS (interrupt translation service). Along with > > > > >> the MSI MSG write transaction, the device outputs a DeviceID conveyed on > > > > >> the bus. This DeviceID (~ your source-ID) enables to index a device > > > > >> table. The entry in the device table points to a DeviceId interrupt > > > > >> translation table indexed by the EventID found in the msi msg. So the > > > > >> entry in the interrupt translation table eventually gives you the > > > > >> eventual interrupt ID targeted by the MSI MSG. > > > > >> This translation capability if not available in GICv2M though, ie. the > > > > >> one I am currently using. > > > > >> > > > > >> Those tables currently are built by the ITS irqchip (irq-gic-v3-its.c) > > > > > > That's right. GICv3/ITS disambiguates the interrupt source using the > > > DeviceID, which for PCI is derived from the Requester ID of the endpoint. > > > GICv2m is less flexible and requires a separate physical frame per guest > > > to achieve isolation. > > > > > We should still support MSI passthrough with a single MSI frame host > > system though, right? > > I think we should treat the frame as an exclusive resource and assign it > to a single VM. so on a single frame GICv2m system, either your host or a single VM gets to do MSIs... > > > (Users should just be aware that guests are not fully protected against > > misbehaving hardware in that case). > > Is it confined to misbehaving hardware? What if a malicious/buggy guest > configures its device to DMA all over the doorbell? > I guess not, I suppose we can't trap any configuration access and mediate that for any device. Bummer. -Christoffer