Hi,
I'm a bit confused by the interface for interacting with the page rmap.
For context, on a TDP-enabled x86-64 host, I'm logging each time a
GFN->PFN mapping is created/modified/removed for a non-MMIO page (kernel
version 5.4).
First, my understanding is that the page rmap is a mapping of non-MMIO
PFNs back to the GFNs that use them. The interface for creating an rmap
entry (and thus, a new GFN->PFN mapping) appears to be rmap_add() and is
quite straightforward. However, rmap_remove() does not appear to be the
(only) function for removing an entry from the page rmap. For instance,
kvm_zap_rmapp()---used by the mmu_notifier for invalidations---jumps
straight to pte_list_remove(), while drop_spte() uses rmap_remove().
Would it be fair to say that mmu_spte_clear_track_bits() is found on all
paths for removing an entry from the page rmap?
Second, for updates to the frame numbers in an existing SPTE, there are
both mmu_set_spte() and mmu_spte_set(). Could someone please clarify the
difference between these functions?
Finally, much of the logic between the page rmap and parent PTE rmaps
(understandably) overlaps. However, with TDP-enabled, I'm not entirely
sure what the role of the parent PTE rmaps is relative to the page rmap.
Could someone possibly clarify?
Thanks, and best wishes,
Kevin
