Commit 70b6d525 authored Apr 30, 2020 by Igor Mammedov Committed by Eduardo Habkost May 12, 2020

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@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>

parent de2f658b

backends/hostmem.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -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");