On Thu, Apr 25, 2024 at 3:12 AM Isaku Yamahata <isaku.yamahata@xxxxxxxxx> wrote: > > > get_user_pages_fast(source addr) > > > read_lock(mmu_lock) > > > kvm_tdp_mmu_get_walk_private_pfn(vcpu, gpa, &pfn); > > > if the page table doesn't map gpa, error. > > > TDH.MEM.PAGE.ADD() > > > TDH.MR.EXTEND() > > > read_unlock(mmu_lock) > > > put_page() > > > > Hmm, KVM doesn't _need_ to use invalidate_lock to protect against guest_memfd > > invalidation, but I also don't see why it would cause problems. The invalidate_lock is only needed to operate on the guest_memfd, but it's a rwsem so there are no risks of lock inversion. > > I.e. why not > > take mmu_lock() in TDX's post_populate() implementation? > > We can take the lock. Because we have already populated the GFN of guest_memfd, > we need to make kvm_gmem_populate() not pass FGP_CREAT_ONLY. Otherwise we'll > get -EEXIST. I don't understand why TDH.MEM.PAGE.ADD() cannot be called from the post-populate hook. Can the code for TDH.MEM.PAGE.ADD be shared between the memory initialization ioctl and the page fault hook in kvm_x86_ops? Paolo > > > That would allow having > > a sanity check that the PFN that guest_memfd() has is indeed the PFN that KVM's > > S-EPT mirror has, i.e. the PFN that KVM is going to PAGE.ADD. > > Because we have PFN from the mirrored EPT, I thought it's duplicate to get PFN > again via guest memfd. We can check if two PFN matches. > -- > Isaku Yamahata <isaku.yamahata@xxxxxxxxx> >
