[Xen-devel] [PATCH 1 of 3] x86/mm: Relieve contention for p2m lock in gva_to_gfn

[Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>]

 xen/arch/x86/mm/hap/guest_walk.c |  6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)


We don't need to hold the p2m lock for the duration of the guest walk. We need
to ensure livenes of the top level page.

Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

diff -r 34c7e6be9265 -r 58fd70123787 xen/arch/x86/mm/hap/guest_walk.c
--- a/xen/arch/x86/mm/hap/guest_walk.c
+++ b/xen/arch/x86/mm/hap/guest_walk.c
@@ -52,6 +52,7 @@ unsigned long hap_p2m_ga_to_gfn(GUEST_PA
 {
     uint32_t missing;
     mfn_t top_mfn;
+    struct page_info *top_page;
     void *top_map;
     p2m_type_t p2mt;
     p2m_access_t p2ma;
@@ -85,13 +86,16 @@ unsigned long hap_p2m_ga_to_gfn(GUEST_PA
 
     /* Map the top-level table and call the tree-walker */
     ASSERT(mfn_valid(mfn_x(top_mfn)));
+    top_page = mfn_to_page(mfn_x(top_mfn));
+    ASSERT(get_page(top_page, p2m->domain));
+    __put_gfn(p2m, top_gfn);
     top_map = map_domain_page(mfn_x(top_mfn));
 #if GUEST_PAGING_LEVELS == 3
     top_map += (cr3 & ~(PAGE_MASK | 31));
 #endif
     missing = guest_walk_tables(v, p2m, ga, &gw, pfec[0], top_mfn, top_map);
     unmap_domain_page(top_map);
-    __put_gfn(p2m, top_gfn);
+    put_page(top_page);
 
     /* Interpret the answer */
     if ( missing == 0 )

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