On 18.07.2016 17:18, Greg Kurz wrote:
> On Mon, 18 Jul 2016 15:19:04 +0200
> Thomas Huth <th...@redhat.com> wrote:
>
>> After already fixing two issues with the huge page detection mechanism
>> (see commit 159d2e39a860 and 86b50f2e1bef), Greg Kurz noticed another
>> case that caused the guest to crash where QEMU announces huge pages
>> though they should not be available for the guest:
>>
>> qemu-system-ppc64 -enable-kvm ... -mem-path /dev/hugepages \
>> -m 1G,slots=4,maxmem=32G
>> -object memory-backend-ram,policy=default,size=1G,id=mem-mem1 \
>> -device pc-dimm,id=dimm-mem1,memdev=mem-mem1 -smp 2 \
>> -numa node,nodeid=0 -numa node,nodeid=1
>>
>> That means if there is a global mem-path option, we still have
>> to look at the memory-backend objects that have been specified
>> additionally and return their minimum page size if that value
>> is smaller than the page size of the main memory.
>>
>> Reported-by: Greg Kurz <gr...@kaod.org>
>> Signed-off-by: Thomas Huth <th...@redhat.com>
>> ---
>
> Just one remark, see below, but apart from that:
>
> Reviewed-by: Greg Kurz <gr...@kaod.org>
> Tested-by: Greg Kurz <gr...@kaod.org>
>
>> target-ppc/kvm.c | 27 ++++++++++++++-------------
>> 1 file changed, 14 insertions(+), 13 deletions(-)
>>
>> diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
>> index 7a8f555..97ab450 100644
>> --- a/target-ppc/kvm.c
>> +++ b/target-ppc/kvm.c
>> @@ -366,10 +366,13 @@ static int find_max_supported_pagesize(Object *obj,
>> void *opaque)
>> static long getrampagesize(void)
>> {
>> long hpsize = LONG_MAX;
>> + long mainrampagesize;
>> Object *memdev_root;
>>
>> if (mem_path) {
>> - return gethugepagesize(mem_path);
>> + mainrampagesize = gethugepagesize(mem_path);
>> + } else {
>> + mainrampagesize = getpagesize();
>> }
>>
>> /* it's possible we have memory-backend objects with
>> @@ -383,28 +386,26 @@ static long getrampagesize(void)
>> * backend isn't backed by hugepages.
>> */
>> memdev_root = object_resolve_path("/objects", NULL);
>> - if (!memdev_root) {
>> - return getpagesize();
>> + if (memdev_root) {
>> + object_child_foreach(memdev_root, find_max_supported_pagesize,
>> &hpsize);
>> }
>> -
>> - object_child_foreach(memdev_root, find_max_supported_pagesize, &hpsize);
>> -
>> - if (hpsize == LONG_MAX || hpsize == getpagesize()) {
>> - return getpagesize();
>> + if (hpsize == LONG_MAX) {
>> + /* No additional memory regions found ==> Report main RAM page size
>> */
>> + return mainrampagesize;
>> }
>>
>> /* 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!
>> + * memory-backend, then there is at least one node using "normal" RAM,
>> + * so if its page size is smaller we have got to report that size
>> instead.
>> */
>> - if (nb_numa_nodes == 0 || numa_info[0].node_memdev == NULL) {
>> + if (hpsize > mainrampagesize &&
>> + (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).");
>
> Maybe update the error message since we have another condition ?
>
> Something like:
>
> "Huge page support disabled (at least one numa uses standard page size)"
That sounds also a little bit confusing since the error message could
occur when there is no numa configured at all. I think refering to "main
memory" is better here so that the users have a chance to know that they
might need to specify the global "-mem-path" parameter here, too.
Thomas
