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hostmem: don't use mbind() if host-nodes is empty

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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@physnet.uni-hamburg.de>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20200430154606.6421-1-imammedo@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
This commit is contained in:
Igor Mammedov 2020-04-30 11:46:06 -04:00 committed by Eduardo Habkost
parent de2f658b6b
commit 70b6d525df
1 changed files with 4 additions and 2 deletions
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6
backends/hostmem.c
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@ -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");