KVM: Ensure memory attributes xarray nodes are accounted to the caller's memcg

Explicitly instantiate the memory attributes xarray with XA_FLAGS_ACCOUNT
to ensure that all allocations are accounted to the memcg.  Frustratingly,
memory allocations done in the "fastpath" do not honor the passed in gfp,
even for an explicit xa_reserve().  Only the rare, slow path __xas_nomem()
honors the original gfp.  E.g.

  xa_reserve(..., GFP_KERNEL_ACCOUNT)
  |
  -> ...
     |
     -> __xa_cmpxchg_raw()
        |
        -> xas_store()  <== does not take @gfp
           |
           -> xas_create()
              |
              -> xas_alloc()

The bug was confirmed by observing that a process in a cgroup limited to
256 MiB grew radix_tree_node slab by ~512 MiB while its memory.current
stayed near 0.

Fixes: 5a475554db1e ("KVM: Introduce per-page memory attributes")
Cc: stable@vger.kernel.org
Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: David Ballesteros <davimaba.v@proton.me>
Link: https://patch.msgid.link/20260915175335.138547-4-davimaba.v@proton.me
[sean: rewrite changelog, tag for stable]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2a046e95f95e..df643ec3ea75 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1117,7 +1117,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 	rcuwait_init(&kvm->mn_memslots_update_rcuwait);
 	xa_init(&kvm->vcpu_array);
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
-	xa_init(&kvm->mem_attr_array);
+	xa_init_flags(&kvm->mem_attr_array, XA_FLAGS_ACCOUNT);
 #endif
 
 	INIT_LIST_HEAD(&kvm->gpc_list);