[PATCH] x86/mm: limit deferred TLB flushing to PV owned pages

[Roger Pau Monne <roger@xxxxxxxxxxxxxx>]

The current logic on x86 will mark all domain owned pages as needed a TLB
flush before being re-used.  However such TLB flushing is only strictly
needed for PV domain owned pages, as those can keep a reference to the page
in the TLB after it has been freed.

Limit the requirement of a flush to pages that are owned by PV domains.

Signed-off-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
---
 xen/common/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 62ac89b824de..be202f0b8d1e 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1501,6 +1501,7 @@ bool scrub_free_pages(void)
 
 static bool mark_page_free(struct page_info *pg, mfn_t mfn)
 {
+    const struct domain *owner = page_get_owner(pg);
     bool pg_offlined = false;
 
     ASSERT(mfn_x(mfn) == mfn_x(page_to_mfn(pg)));
@@ -1539,7 +1540,7 @@ static bool mark_page_free(struct page_info *pg, mfn_t 
mfn)
     }
 
     /* If a page has no owner it will need no safety TLB flush. */
-    pg->u.free.need_tlbflush = (page_get_owner(pg) != NULL);
+    pg->u.free.need_tlbflush = owner && is_pv_domain(owner);
     if ( pg->u.free.need_tlbflush )
         page_set_tlbflush_timestamp(pg);
 
-- 
2.55.0