From d4ea410ce4b8aa46a316476ea2624a357bf31fa9 Mon Sep 17 00:00:00 2001 From: "Gregory Price (Meta)" Date: Sat, 17 Oct 2026 22:33:49 -0400 Subject: [PATCH] mm/mempolicy: apply bind policies against the scoped allocation zone QEMU fails to start a guest with a VFIO device when guest RAM comes from a memory backend bound to a movable-only node: vfio_container_dma_map(0x55b1b1317800, 0x0, 0x10000000, 0x7f39a2200000) = -12 (Cannot allocate memory) VFIO pins guest RAM when the device is realized, and the pin faults the pages in. io_uring fixed buffers fail the same way. Faulting the range in before pinning lets the same pin succeed, since resident pages are migrated off the node instead. A long-term pin faults under memalloc_pin_save(). PF_MEMALLOC_PIN makes current_gfp_context() clear __GFP_MOVABLE, but policy_nodemask() tests apply_policy_zone() against the caller's gfp. The bind keeps its movable-only nodemask, and the allocation finds no usable zone: page allocation failure: order:0, mode:0x140dc2(GFP_HIGHUSER|__GFP_ZERO|__GFP_COMP), nodemask=1,cpuset=/,mems_allowed=0-1 Call Trace: warn_alloc+0x136/0x150 __alloc_frozen_pages_noprof+0xed8/0x1720 alloc_pages_mpol+0xaa/0x170 vma_alloc_folio_noprof+0x65/0xd0 __handle_mm_fault+0x137b/0x1ac0 handle_mm_fault+0xa0/0x270 __get_user_pages+0x250/0xfd0 __gup_longterm_locked+0x116/0x870 gup_fast_fallback+0xcfc/0xdf0 pin_user_pages_fast+0x47/0x60 io_pin_pages+0x9a/0x110 Base page faults fail with -ENOMEM. hugetlb faults fail with -EFAULT. Check the policy zone against current_gfp_context(gfp), so a pin-scoped fault falls back off the movable-only nodemask, like any other non-movable allocation under the same bind. Tested in qemu with a dax/kmem movable-only node 1. io_uring and VFIO pins of unfaulted base pages and 2MB hugetlb pages now succeed and land on node 0 (correct). QEMU now starts with the same backend binding. Link: https://lore.kernel.org/20261018023349.1697434-1-gourry@gourry.net Fixes: 8e3560d963d2 ("mm: honor PF_MEMALLOC_PIN for all movable pages") Signed-off-by: Gregory Price (Meta) Signed-off-by: Andrew Morton Reviewed-by: Joshua Hahn Cc: David Hildenbrand Cc: Zi Yan Cc: Rakie Kim Cc: Ying Huang Cc: Pasha Tatashin Cc: Michal Hocko Cc: --- mm/mempolicy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 70298fded1b4..0884c629670d 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2302,7 +2302,7 @@ static nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *pol, break; case MPOL_BIND: /* Restrict to nodemask (but not on lower zones) */ - if (apply_policy_zone(pol, gfp_zone(gfp)) && + if (apply_policy_zone(pol, gfp_zone(current_gfp_context(gfp))) && cpuset_nodemask_valid_mems_allowed(&pol->nodes)) nodemask = &pol->nodes; if (pol->home_node != NUMA_NO_NODE)