On 15.07.2016 10:35, David Gibson wrote: > On Fri, Jul 15, 2016 at 10:10:25AM +0200, Thomas Huth wrote: >> Commit 86b50f2e1bef ("Disable huge page support if it is not available >> for main RAM") already made sure that huge page support is not announced >> to the guest if the normal RAM of non-NUMA configurations is not backed >> by a huge page filesystem. However, there is one more case that can go >> wrong: NUMA is enabled, but the RAM of the NUMA nodes are not configured >> with huge page support (and only the memory of a DIMM is configured with >> it). When QEMU is started with the following command line for example, >> the Linux guest currently crashes because it is trying to use huge pages >> on a memory region that does not support huge pages: >> >> qemu-system-ppc64 -enable-kvm ... -m 1G,slots=4,maxmem=32G -object \ >> >> memory-backend-file,policy=default,mem-path=/hugepages,size=1G,id=mem-mem1 \ >> -device pc-dimm,id=dimm-mem1,memdev=mem-mem1 -smp 2 \ >> -numa node,nodeid=0 -numa node,nodeid=1 >> >> To fix this issue, we've got to make sure to disable huge page support, >> too, when there is a NUMA node that is not using a memory backend with >> huge page support. >> >> Fixes: 86b50f2e1befc33407bdfeb6f45f7b0d2439a740 >> Signed-off-by: Thomas Huth <th...@redhat.com> >> --- >> target-ppc/kvm.c | 10 +++++++--- >> 1 file changed, 7 insertions(+), 3 deletions(-) >> >> diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c >> index 884d564..7a8f555 100644 >> --- a/target-ppc/kvm.c >> +++ b/target-ppc/kvm.c >> @@ -389,12 +389,16 @@ static long getrampagesize(void) >> >> object_child_foreach(memdev_root, find_max_supported_pagesize, &hpsize); >> >> - if (hpsize == LONG_MAX) { >> + if (hpsize == LONG_MAX || hpsize == getpagesize()) { >> return getpagesize(); >> } >> >> - if (nb_numa_nodes == 0 && hpsize > getpagesize()) { >> - /* No NUMA nodes and normal RAM without -mem-path ==> no huge >> pages! */ >> + /* If NUMA is disabled or the NUMA nodes are not backed with a >> + * memory-backend, then there is at least one node using "normal" >> + * RAM. And since normal RAM has not been configured with "-mem-path" >> + * (what we've checked earlier here already), we can not use huge pages! >> + */ >> + if (nb_numa_nodes == 0 || numa_info[0].node_memdev == NULL) { > > Is that second clause sufficient, or do you need to loop through and > check the memdev of every node?
Checking the first entry should be sufficient. QEMU forces you to specify either a memory backend for all NUMA nodes (which we should have looked at during the object_child_foreach() some lines earlier), or you must not specify a memory backend for any NUMA node at all. You can not mix the settings, so checking numa_info[0] is enough. Thomas
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