On Thu, Sep 27, 2018 at 02:07:58PM +1000, David Gibson wrote: > On Fri, Sep 21, 2018 at 08:01:56PM +1000, Paul Mackerras wrote: > > From: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx> > > > > When a host (L0) page which is mapped into a (L1) guest is in turn > > mapped through to a nested (L2) guest we keep a reverse mapping (rmap) > > so that these mappings can be retrieved later. > > > > Whenever we create an entry in a shadow_pgtable for a nested guest we > > create a corresponding rmap entry and add it to the list for the > > L1 guest memslot at the index of the L1 guest page it maps. This means > > at the L1 guest memslot we end up with lists of rmaps as follows; > > > > memslot (L1) > > ----------------- > > | gfn = 0 | -> rmap -> rmap -> rmap -> NULL > > ----------------- > > | gfn = 1 | > > ----------------- > > | gfn = 2 | -> rmap -> NULL > > ----------------- > > | gfn = 3 | -> rmap -> rmap -> NULL > > ----------------- > > | gfn = 4 | > > ----------------- > > | gfn = n | > > ----------------- > > > > When we are notified of a host page being invalidated which has been > > mapped through to a (L1) guest, we can then walk the rmap list for that > > guest page, and find and invalidate all of the corresponding > > shadow_pgtable entries. > > > > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx> > > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx> > > Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> > > Am I right in thinking that the reason we need this in addition to the > exiting rmap for the L1 guest is that we need to know the LPID(s) to > invalidate in the case of a host invalidation? The existing rmap is not really used for radix guests because we get a guest real address and we can just index into the partition-scoped radix tree and find the one and only PTE that maps that guest real address. With a nested guest, a given L1 guest real page could be mapped in the shadow partition-scoped trees for multiple nested guests at arbitrary L2 guest real addresses. The rmap that we implement here gives us a list of (l1 lpid, l2 guest real address) combinations that (may) map the target L1 guest real page. Paul.
