[qemu-xen staging-4.14] hostmem: don't use mbind() if host-nodes is empty

[patchbot@xxxxxxx]

commit 9e6e3ba30984267be4721022f579fb168d43c8a4
Author:     Igor Mammedov <imammedo@xxxxxxxxxx>
AuthorDate: Thu Apr 30 11:46:06 2020 -0400
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon Aug 24 18:55:30 2020 -0500

    hostmem: don't use mbind() if host-nodes is empty
    
    Since 5.0 QEMU uses hostmem backend for allocating main guest RAM.
    The backend however calls mbind() which is typically NOP
    in case of default policy/absent host-nodes bitmap.
    However when runing in container with black-listed mbind()
    syscall, QEMU fails to start with error
     "cannot bind memory to host NUMA nodes: Operation not permitted"
    even when user hasn't provided host-nodes to pin to explictly
    (which is the case with -m option)
    
    To fix issue, call mbind() only in case when user has provided
    host-nodes explicitly (i.e. host_nodes bitmap is not empty).
    That should allow to run QEMU in containers with black-listed
    mbind() without memory pinning. If QEMU provided memory-pinning
    is required user still has to white-list mbind() in container
    configuration.
    
    Reported-by: Manuel Hohmann <mhohmann@xxxxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx>
    Message-Id: <20200430154606.6421-1-imammedo@xxxxxxxxxx>
    Tested-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
    Cc: qemu-stable@xxxxxxxxxx
    Signed-off-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
    (cherry picked from commit 70b6d525dfb51d5e523d568d1139fc051bc223c5)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 backends/hostmem.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/backends/hostmem.c b/backends/hostmem.c
index 327f9eebc3..0efd7b7bd6 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -383,8 +383,10 @@ host_memory_backend_memory_complete(UserCreatable *uc, 
Error **errp)
         assert(sizeof(backend->host_nodes) >=
                BITS_TO_LONGS(MAX_NODES + 1) * sizeof(unsigned long));
         assert(maxnode <= MAX_NODES);
-        if (mbind(ptr, sz, backend->policy,
-                  maxnode ? backend->host_nodes : NULL, maxnode + 1, flags)) {
+
+        if (maxnode &&
+            mbind(ptr, sz, backend->policy, backend->host_nodes, maxnode + 1,
+                  flags)) {
             if (backend->policy != MPOL_DEFAULT || errno != ENOSYS) {
                 error_setg_errno(errp, errno,
                                  "cannot bind memory to host NUMA nodes");
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#staging-4.14