Borislav Petkov wrote: > On Wed, Sep 07, 2022 at 09:52:17AM -0700, Dan Williams wrote: > > To be clear nfit stuff and CXL does run in guests, but they do not > > support secure-erase in a guest. > > > > However, the QEMU CXL enabling is building the ability to do *guest > > physical* address space management, but in that case the driver can be > > paravirtualized to realize that it is not managing host-physical address > > space and does not need to flush caches. That will need some indicator > > to differentiate virtual CXL memory expanders from assigned devices. > > Sounds to me like that check should be improved later to ask > whether the kernel is managing host-physical address space, maybe > arch_flush_memregion() should check whether the address it is supposed > to flush is host-physical and exit early if not...
Even though I raised the possibility of guest passthrough of a CXL memory expander, I do not think it could work in practice without it being a gigantic security nightmare. So it is probably safe to just do the hypervisor check and assume that there's no such thing as guest management of host physical address space.
