[PATCH V3 kvm-x86/gmem 1/2] KVM: guest_memfd: move kvm_gmem_get_index() and use in kvm_gmem_prepare_folio()

[Shivank Garg <shivankg@amd.com>]

Move kvm_gmem_get_index() to the top of the file so that it can be used
in kvm_gmem_prepare_folio() to replace the open-coded calculation.

No functional change intended.

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---

Changelog:
V3:
- Split into distinct patches per Sean's feedback, drop whitespace and
  ULONG_MAX change.
V2:
- https://lore.kernel.org/all/20250902080307.153171-2-shivankg@amd.com
- Incorporate David's suggestions.
V1:
- https://lore.kernel.org/all/20250901051532.207874-3-shivankg@amd.com

 virt/kvm/guest_memfd.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index fbca8c0972da..22dacf49a04d 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -25,6 +25,11 @@ static inline kvm_pfn_t folio_file_pfn(struct folio *folio, pgoff_t index)
 	return folio_pfn(folio) + (index & (folio_nr_pages(folio) - 1));
 }
 
+static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
+{
+	return gfn - slot->base_gfn + slot->gmem.pgoff;
+}
+
 static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
 				    pgoff_t index, struct folio *folio)
 {
@@ -78,7 +83,7 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
 	 * checked when creating memslots.
 	 */
 	WARN_ON(!IS_ALIGNED(slot->gmem.pgoff, 1 << folio_order(folio)));
-	index = gfn - slot->base_gfn + slot->gmem.pgoff;
+	index = kvm_gmem_get_index(slot, gfn);
 	index = ALIGN_DOWN(index, 1 << folio_order(folio));
 	r = __kvm_gmem_prepare_folio(kvm, slot, index, folio);
 	if (!r)
@@ -335,11 +340,6 @@ static inline struct file *kvm_gmem_get_file(struct kvm_memory_slot *slot)
 	return get_file_active(&slot->gmem.file);
 }
 
-static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
-{
-	return gfn - slot->base_gfn + slot->gmem.pgoff;
-}
-
 static bool kvm_gmem_supports_mmap(struct inode *inode)
 {
 	const u64 flags = (u64)inode->i_private;
-- 
2.43.0