On Wed, Apr 27, 2016 at 04:56:32PM +0200, Joerg Roedel wrote: > On Wed, Apr 27, 2016 at 05:34:30PM +0300, Michael S. Tsirkin wrote: > > On Wed, Apr 27, 2016 at 04:23:32PM +0200, Joerg Roedel wrote: > > > QEMU can choose to bypass IOMMU for one device and not the other. > > IOMMU in QEMU isn't involved when it's bypassed. > > And it is QEMU's task to tell the OS, right? And the correct way to do > this is via the firmware ACPI tables. Going forward, this might be reasonable. Of course it didn't in the past and no one cared because virtio devices used physical addresses. We have to keep these setups working. > > Fine but this is beside the point. Almost all virtio devices > > bypass IOMMU and what this patch does is create a way > > to detect devices that don't. This code can maybe go into > > platform. > > Again, the way to detect this is in platform code must not be device > specific. This is what the DMAR and IVRS tables on x86 are for. > > When there is no way to do this in the firmware (or there is no firmware > at all), we have to do a quirk in the platform code for it. > > > > Joerg I really don't get it. There's exactly one device that works now and needs the work-around and so that we need to support, and that is virtio. It happens to have exactly the same issue on all platforms. Why would we want to work hard to build platform-specific solutions to a problem that can be solved in 5 lines of generic code? -- MST -- 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
