From: Michael S. Tsirkin Date: Wed, 3 Jun 2026 15:57:33 +0000 (-0400) Subject: KVM: guest_memfd: fix NUMA interleave index double-counting X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=48dbe473219832788c3940c84faa7f1df4375d5d;p=thirdparty%2Fkernel%2Flinux.git KVM: guest_memfd: fix NUMA interleave index double-counting kvm_gmem_get_policy() sets the interleave index (the output param that's typically named "ilx") to the full page offset (vm_pgoff + vma offset). But get_vma_policy() adds the page offset on top of the interleave index, and so the offset is counted twice. This causes NUMA interleaving to skip nodes: for order-0 pages the effective index jumps by 2 for each consecutive page. The vm_op.get_policy() implementation should return only a per-file bias in the interleave index (like shmem_get_policy does with inode->i_ino), letting get_vma_policy() add the page-offset component. Fix by setting the output interleave index to the inode number (a la shmem) instead of the full page offset, as the index is intended to be a constant, semi-random value for a given file, e.g. so that interleaving doesn't start at the same node for every file, and so that allocations are round-robined across nodes based on the page offset (the selected node would bounce/skip around if the index isn't constant). Found by Sashiko (sashiko.dev) AI code review. Fixes: ed1ffa810bd6 ("KVM: guest_memfd: Enforce NUMA mempolicy using shared policy") Cc: Sean Christopherson Cc: Paolo Bonzini Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Michael S. Tsirkin Acked-by: David Hildenbrand (Arm) Reviewed-by: Shivank Garg Tested-by: Shivank Garg Fixes: 7f3779a3ac3e ("mm/filemap: Add NUMA mempolicy support to filemap_alloc_folio()") Link: https://patch.msgid.link/0eff0a90667b900bee837d06b5db5025e1f304b5.1780501924.git.mst@redhat.com [sean: use reverse fir-tree, massage changelog] Signed-off-by: Sean Christopherson --- diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index f54502640b08..557aac91fc0a 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -438,11 +438,12 @@ static int kvm_gmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpo } static struct mempolicy *kvm_gmem_get_policy(struct vm_area_struct *vma, - unsigned long addr, pgoff_t *pgoff) + unsigned long addr, pgoff_t *ilx) { + pgoff_t pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT); struct inode *inode = file_inode(vma->vm_file); - *pgoff = vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT); + *ilx = inode->i_ino; /* * Return the memory policy for this index, or NULL if none is set. @@ -453,7 +454,7 @@ static struct mempolicy *kvm_gmem_get_policy(struct vm_area_struct *vma, * can then replace NULL with the default memory policy instead of the * current task's memory policy. */ - return mpol_shared_policy_lookup(&GMEM_I(inode)->policy, *pgoff); + return mpol_shared_policy_lookup(&GMEM_I(inode)->policy, pgoff); } #endif /* CONFIG_NUMA */