[Xen-changelog] [xen master] tools/libs/call: linux: touch newly allocated pages after madvise lockdown

[patchbot@xxxxxxx]

commit b0074ce6a10fd7d6734c4bbb6d6e04910db92152
Author:     Ian Campbell <ian.campbell@xxxxxxxxxx>
AuthorDate: Mon Dec 14 16:46:26 2015 +0000
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Fri Jan 22 12:24:21 2016 +0000

    tools/libs/call: linux: touch newly allocated pages after madvise lockdown
    
    This avoids a potential issue with a fork after allocation but before
    madvise.
    
    Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
    Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libs/call/linux.c |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/tools/libs/call/linux.c b/tools/libs/call/linux.c
index 3641e41..651f380 100644
--- a/tools/libs/call/linux.c
+++ b/tools/libs/call/linux.c
@@ -88,7 +88,7 @@ void *osdep_alloc_pages(xencall_handle *xcall, size_t npages)
 {
     size_t size = npages * PAGE_SIZE;
     void *p;
-    int rc, saved_errno;
+    int rc, i, saved_errno;
 
     /* Address returned by mmap is page aligned. */
     p = mmap(NULL, size, PROT_READ|PROT_WRITE, 
MAP_PRIVATE|MAP_ANONYMOUS|MAP_LOCKED, -1, 0);
@@ -107,6 +107,18 @@ void *osdep_alloc_pages(xencall_handle *xcall, size_t 
npages)
         goto out;
     }
 
+    /*
+     * Touch each page in turn to force them to be un-CoWed, in case a
+     * fork happened in another thread at an inopportune moment
+     * above. The madvise() will prevent any subsequent fork calls from
+     * causing the same problem.
+     */
+    for ( i = 0; i < npages ; i++ )
+    {
+        char *c = (char *)p + (i*PAGE_SIZE);
+        *c = 0;
+    }
+
     return p;
 
 out:
--
generated by git-patchbot for /home/xen/git/xen.git#master

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