On Tue, Mar 12, 2024, Kai Huang wrote: > > Wait. KVM doesn't *need* to do PAGE.ADD from deep in the MMU. The only inputs to > > PAGE.ADD are the gfn, pfn, tdr (vm), and source. The S-EPT structures need to be > > pre-built, but when they are built is irrelevant, so long as they are in place > > before PAGE.ADD. > > > > Crazy idea. For TDX S-EPT, what if KVM_MAP_MEMORY does all of the SEPT.ADD stuff, > > which doesn't affect the measurement, and even fills in KVM's copy of the leaf EPTE, > > but tdx_sept_set_private_spte() doesn't do anything if the TD isn't finalized? > > > > Then KVM provides a dedicated TDX ioctl(), i.e. what is/was KVM_TDX_INIT_MEM_REGION, > > to do PAGE.ADD. KVM_TDX_INIT_MEM_REGION wouldn't need to map anything, it would > > simply need to verify that the pfn from guest_memfd() is the same as what's in > > the TDP MMU. > > One small question: > > What if the memory region passed to KVM_TDX_INIT_MEM_REGION hasn't been pre- > populated? If we want to make KVM_TDX_INIT_MEM_REGION work with these regions, > then we still need to do the real map. Or we can make KVM_TDX_INIT_MEM_REGION > return error when it finds the region hasn't been pre-populated? Return an error. I don't love the idea of bleeding so many TDX details into userspace, but I'm pretty sure that ship sailed a long, long time ago.
