On Fri, Dec 31, 2021, Chao Peng wrote: > On Fri, Dec 24, 2021 at 12:13:51PM +0800, Chao Peng wrote: > > On Thu, Dec 23, 2021 at 06:06:19PM +0000, Sean Christopherson wrote: > > > On Thu, Dec 23, 2021, Chao Peng wrote: > > > > This new function establishes the mapping in KVM page tables for a > > > > given gfn range. It can be used in the memory fallocate callback for > > > > memfd based memory to establish the mapping for KVM secondary MMU when > > > > the pages are allocated in the memory backend. > > > > > > NAK, under no circumstance should KVM install SPTEs in response to allocating > > > memory in a file. The correct thing to do is to invalidate the gfn range > > > associated with the newly mapped range, i.e. wipe out any shared SPTEs associated > > > with the memslot. > > > > Right, thanks. > > BTW, I think the current fallocate() callback is just useless as long as > we don't want to install KVM SPTEs in response to allocating memory in a > file. The invalidation of the shared SPTEs should be notified through > mmu_notifier of the shared memory backend, not memfd_notifier of the > private memory backend. No, because the private fd is the final source of truth as to whether or not a GPA is private, e.g. userspace may choose to not unmap the shared backing. KVM's rule per Paolo's/this proposoal is that a GPA is private if it has a private memslot and is present in the private backing store. And the other core rule is that KVM must never map both the private and shared variants of a GPA into the guest.
