On 2016-03-01 21:39, Michael S. Tsirkin wrote: > On Tue, Mar 01, 2016 at 09:17:58PM +0100, Jan Kiszka wrote: >> On 2016-03-01 21:11, Michael S. Tsirkin wrote: >>> >>> 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. >> >> Exactly, but that's nothing new, is it? It's "just" slow, like other >> shadow MMUs. >> >> Jan > > Well AFAIK KVM does not have such an option ATM: MMIO causes exits for > reads and writes. We want MMIO exits for writes but not reads. > I agree it should be easy to implement.
We have read-only memory slot support for quite a while. It's used to support execute (and read) from emulated ROM devices. Jan -- Siemens AG, Corporate Technology, CT RDA ITP SES-DE Corporate Competence Center Embedded Linux
