On Tue, Apr 5, 2022, at 11:30 AM, Sean Christopherson wrote:

On Tue, Apr 05, 2022, Andy Lutomirski wrote:

quoted

resume guest
*** host -> hypervisor -> guest ***
Guest unshares the page.
*** guest -> hypervisor ***
Hypervisor removes PTE.  TLBI.
*** hypervisor -> guest ***

Obviously considerable cleverness is needed to make a virt IOMMU like this
work well, but still.

Anyway, my suggestion is that the fd backing proposal get slightly modified
to get it ready for multiple subtypes of backing object, which should be a
pretty minimal change.  Then, if someone actually needs any of this
cleverness, it can be added later.  In the mean time, the
pread()/pwrite()/splice() scheme is pretty good.

Tangentially related to getting private-fd ready for multiple things, 
what about
implementing the pread()/pwrite()/splice() scheme in pKVM itself?  I.e. 
read() on
the VM fd, with the offset corresponding to gfn in some way.

Hmm, could make sense.