On Tue, Mar 01, 2016 at 03:00:09PM +0100, Jan Kiszka wrote: > On 2016-03-01 14:48, Jan Kiszka wrote: > > There is likely no way around write-protecting the IOMMU page tables (in > > KVM mode) once we evaluated and cached them somewhere. > > I mean, when in kvm mode AND having something that caches enabled, of > course.
Just write-protecting won't be enough either, since the moment you remove the protection, all bets are off, and if you don't, guest will start from the same point when you re-enter and fault again. What this seems to call for is a new kind of protection where yes PTE is write protected, but instead of making PTE writeable (or killing guest) KVM handles it as an MMIO: emulates the write and then skips the instruction. Emulation can be in kernel, just writing into guest memory on behalf of the guest - with some kind of notifier to flush the vfio cache - or instead it can exit to userspace and have QEMU handle it like MMIO and write into guest memory. > Besides vfio, we also still have the question how to deal with virtio > and DMA remapping, which is probably similarly complicated when some > vhost technology is involved. > > Jan Well, that can limit itself to cache valid entries which is presumably what hardware iommu does. > -- > Siemens AG, Corporate Technology, CT RDA ITP SES-DE > Corporate Competence Center Embedded Linux
