On Tue, Mar 01, 2016 at 10:23:55PM +0100, Jan Kiszka wrote: > 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
I didn't realize this causes an mmio exit. > -- > Siemens AG, Corporate Technology, CT RDA ITP SES-DE > Corporate Competence Center Embedded Linux
