On Mon, Jul 18, 2016 at 10:59:44AM +0200, Greg Kurz wrote: > On Mon, 18 Jul 2016 10:52:36 +1000 > David Gibson <[email protected]> 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 <[email protected]> > > > --- > > > target-ppc/kvm.c | 10 +++++++--- > > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > Applied to ppc-for-2.7, thanks. > > > > It looks like my replies to this patch were ignored... no big deal > though :)
I saw them. IIUC, though, this patch still improves the situation,
even if it doesn't get every case right, so I was inclined to include
it earlier rather than later.
>
> > >
> > > 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) {
> > > static bool warned;
> > > if (!warned) {
> > > error_report("Huge page support disabled (n/a for main
> > > memory).");
> >
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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