From: Paolo Bonzini Date: Thu, 4 Apr 2024 17:25:19 +0000 (-0400) Subject: KVM: guest_memfd: limit overzealous WARN X-Git-Tag: block-6.11-20240726~19^2~4^2~22^2~5 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=fa30b0dc91c815b9579d6f758437c35db059f5ae;p=linux-block.git KVM: guest_memfd: limit overzealous WARN Because kvm_gmem_get_pfn() is called from the page fault path without any of the slots_lock, filemap lock or mmu_lock taken, it is possible for it to race with kvm_gmem_unbind(). This is not a problem, as any PTE that is installed temporarily will be zapped before the guest has the occasion to run. However, it is not possible to have a complete unbind+bind racing with the page fault, because deleting the memslot will call synchronize_srcu_expedited() and wait for the page fault to be resolved. Thus, we can still warn if the file is there and is not the one we expect. Signed-off-by: Paolo Bonzini --- diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index c27828b0d42d..fd32288d0fbc 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -499,7 +499,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, gmem = file->private_data; - if (WARN_ON_ONCE(xa_load(&gmem->bindings, index) != slot)) { + if (xa_load(&gmem->bindings, index) != slot) { + WARN_ON_ONCE(xa_load(&gmem->bindings, index)); r = -EIO; goto out_fput; }