[RFC PATCH v4 12/25] KVM: guest_memfd: Invalidate mappings before memslot unbind

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

Use the generic invalidate_start/end helpers to remove shared and
private device mappings before removing the memslot's guest_memfd
binding.

Hold gmem_provider_lock() across invalidation and binding removal to
prevent device unlock from racing with teardown.

Keep the file attributes and has_private_ranges unchanged. Deleting a
memslot removes mappings but does not share the backing range. Device
unlock remains blocked until userspace shares the private ranges or
closes the last guest_memfd reference.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: kvm@vger.kernel.org
Cc: patches@lists.linux.dev
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 virt/kvm/guest_memfd.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index d3de2e7bb9f5..870fe11c1c5c 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1873,6 +1873,8 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot)
 	unsigned long start = slot->gmem.pgoff;
 	unsigned long end = start + slot->npages;
 	struct gmem_file *f;
+	struct gmem_inode *gi;
+	enum kvm_gfn_range_filter filter;
 
 	/*
 	 * Nothing to do if the underlying file was _already_ closed, as
@@ -1892,8 +1894,13 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot)
 	 * drops slots_lock, so there's no need to verify the file is live.
 	 */
 	f = file->private_data;
+	gi = GMEM_I(file_inode(file));
+	filter = kvm_gmem_get_all_gfns_filter(file_inode(file));
 
 	filemap_invalidate_lock(file->f_mapping);
+	gmem_provider_lock(gi);
+	__kvm_gmem_invalidate_start(f, start, end, filter);
+	__kvm_gmem_invalidate_end(f, start, end);
 	xa_store_range(&f->bindings, start, end - 1, NULL, GFP_KERNEL);
 
 	/*
@@ -1902,6 +1909,7 @@ void kvm_gmem_unbind(struct kvm_memory_slot *slot)
 	 * to guarantee kvm_gmem_get_pfn() can't see the slot+file.
 	 */
 	WRITE_ONCE(slot->gmem.file, NULL);
+	gmem_provider_unlock(gi);
 	filemap_invalidate_unlock(file->f_mapping);
 }
 
-- 
2.43.0