xen: mapcache: Fix finding matching entry

Commit Message

Aleksandr Partanen April 10, 2025, 2:46 p.m. UTC

If we have request without lock and hit unlocked or invalid
entry during the search, we remap it immediately,
even if we have matching entry in next entries in bucket.
This leads to duplication of mappings of the same size,
and to possibility of selecting the wrong element
during invalidation and underflow it's entry->lock counter

Signed-off-by: Aleksandr Partanen <[e-mail]>
---
 hw/xen/xen-mapcache.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Patch

diff --git a/hw/xen/xen-mapcache.c b/hw/xen/xen-mapcache.c
index 698b5c53ed..2c8f861fdb 100644
--- a/hw/xen/xen-mapcache.c
+++ b/hw/xen/xen-mapcache.c
@@ -376,12 +376,12 @@  tryagain:
 
     entry = &mc->entry[address_index % mc->nr_buckets];
 
-    while (entry && (lock || entry->lock) && entry->vaddr_base &&
-            (entry->paddr_index != address_index || entry->size != cache_size ||
+    while (entry && (!entry->vaddr_base ||
+            entry->paddr_index != address_index || entry->size != cache_size ||
              !test_bits(address_offset >> XC_PAGE_SHIFT,
                  test_bit_size >> XC_PAGE_SHIFT,
                  entry->valid_mapping))) {
-        if (!free_entry && !entry->lock) {
+        if (!free_entry && (!entry->lock || !entry->vaddr_base)) {
             free_entry = entry;
             free_pentry = pentry;
         }