On Thu, 8 Dec 2016 13:14:04 +0000 Robin Murphy <robin.murphy@xxxxxxx> wrote: > On 08/12/16 09:36, Auger Eric wrote: > > 3) RMRR reporting in the iommu group sysfs? Joerg: yes; Don: no > > My current series does not expose them in iommu group sysfs. > > I understand we can expose the RMRR regions in the iomm group sysfs > > without necessarily supporting RMRR requiring device assignment. > > We can also add this support later. > > As you say, reporting them doesn't necessitate allowing device > assignment, and it's information which can already be easily grovelled > out of dmesg (for intel-iommu at least) - there doesn't seem to be any > need to hide them, but the x86 folks can have the final word on that. Eric and I talked about this and I don't see the value in identifying an RMRR as anything other than a reserved range for a device. It's not userspace's job to maintain an identify mapped range for the device, and it can't be trusted to do so anyway. It does throw a kink in the machinery though as an RMRR is a reserved memory range unique to a device. It doesn't really fit into a monolithic /sys/class/iommu view of global reserved regions as an RMRR is only relevant to the device paths affected. Another kink is that sometimes we know what the RMRR is for, know that it's irrelevant for our use case, and ignore it. This is true for USB and Intel graphics use cases of RMRRs. Also, aside from the above mentioned cases, devices with RMRRs are currently excluded from participating in the IOMMU API by the intel-iommu driver and I expect this to continue in the general case regardless of whether the ranges are more easily exposed to userspace. ARM may have to deal with mangling a guest memory map due to lack of any standard layout, de facto or otherwise, but for x86 I don't think it's worth the migration and hotplug implications. Thanks, Alex -- 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
