[Xen-changelog] [qemu-xen stable-4.12] xen-mapcache: use MAP_FIXED flag so the mmap address hint is always honored

[patchbot@xxxxxxx]

commit af88bba0d28a489e713676fb7925f331c63e58ab
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Mar 18 18:37:31 2019 +0100
Commit:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
CommitDate: Mon Mar 25 17:04:57 2019 +0000

    xen-mapcache: use MAP_FIXED flag so the mmap address hint is always honored
    
    Or if it's not possible to honor the hinted address an error is returned
    instead. This makes it easier to spot the actual failure, instead of
    failing later on when the caller of xen_remap_bucket realizes the
    mapping has not been created at the requested address.
    
    Also note that at least on FreeBSD using MAP_FIXED will cause mmap to
    try harder to honor the passed address.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Acked-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    Reviewed-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Message-Id: <20190318173731.14494-1-roger.pau@xxxxxxxxxx>
    Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    (cherry picked from commit 4158e93f4aced247c8db94a0275fc027da7dc97e)
---
 hw/i386/xen/xen-mapcache.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c
index 4e4f069a24..d843325d1a 100644
--- a/hw/i386/xen/xen-mapcache.c
+++ b/hw/i386/xen/xen-mapcache.c
@@ -184,9 +184,14 @@ static void xen_remap_bucket(MapCacheEntry *entry,
         pfns[i] = (address_index << (MCACHE_BUCKET_SHIFT-XC_PAGE_SHIFT)) + i;
     }
 
+    /*
+     * If the caller has requested the mapping at a specific address use
+     * MAP_FIXED to make sure it's honored.
+     */
     if (!dummy) {
         vaddr_base = xenforeignmemory_map2(xen_fmem, xen_domid, vaddr,
-                                           PROT_READ | PROT_WRITE, 0,
+                                           PROT_READ | PROT_WRITE,
+                                           vaddr ? MAP_FIXED : 0,
                                            nb_pfn, pfns, err);
         if (vaddr_base == NULL) {
             perror("xenforeignmemory_map2");
@@ -198,7 +203,8 @@ static void xen_remap_bucket(MapCacheEntry *entry,
          * mapping immediately due to certain circumstances (i.e. on resume 
now)
          */
         vaddr_base = mmap(vaddr, size, PROT_READ | PROT_WRITE,
-                          MAP_ANON | MAP_SHARED, -1, 0);
+                          MAP_ANON | MAP_SHARED | (vaddr ? MAP_FIXED : 0),
+                          -1, 0);
         if (vaddr_base == MAP_FAILED) {
             perror("mmap");
             exit(-1);
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.12

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