From 6233b679cae8741890f981c9dd6570d47715141e Mon Sep 17 00:00:00 2001 From: David Gibson Date: Thu, 19 Apr 2018 17:19:11 +1000 Subject: [PATCH] Clear mem_path if we fall back to anonymous RAM allocation If the -mem-path option is set, we attempt to map the guest's RAM from a file in the given path; it's usually used to back guest RAM with hugepages. If we're unable to (e.g. not enough free hugepages) then we fall back to allocating normal anonymous pages. This behaviour can be surprising, but a comment in allocate_system_memory_nonnuma() suggests it's legacy behaviour we can't change. What really isn't ok, though, is that in this case we leave mem_path set. That means functions which attempt to determine the pagesize of main RAM can erroneously think it is hugepage based on the requested path, even though it's not. This is particular bad for the pseries machine type. KVM HV limitations mean the guest can't use pagesizes larger than the host page size used to back RAM. That means that such a fallback, rather than merely giving poorer performance than expected will cause the guest to freeze up early in boot as it attempts to use large page mappings that can't work. This patch addresses the problem by clearing the mem_path variable when we fall back to anonymous pages, meaning that subsequent attempts to determine the RAM page size will get an accurate result. Signed-off-by: David Gibson --- numa.c | 1 + 1 file changed, 1 insertion(+) diff --git a/numa.c b/numa.c index 1116c90af9..78a869e598 100644 --- a/numa.c +++ b/numa.c @@ -469,6 +469,7 @@ static void allocate_system_memory_nonnuma(MemoryRegion *mr, Object *owner, /* Legacy behavior: if allocation failed, fall back to * regular RAM allocation. */ + mem_path = NULL; memory_region_init_ram_nomigrate(mr, owner, name, ram_size, &error_fatal); } #else -- 2.11.4.GIT