[PATCH v4 13/17] [GMEM-DEPENDENT] KVM: guest_memfd: Add helpers to get start/end gfns give gmem+slot+pgoff

[Yan Zhao <yan.y.zhao@intel.com>]

From: Sean Christopherson <seanjc@google.com>

Add helpers for getting a gfn given a gmem slot+pgoff, and for getting a
gfn given a starting or ending pgoff, i.e. an offset that may be beyond
the range of the memslot binding.  Providing helpers will avoid duplicate
boilerplate code "if" future code also needs to iterate over gfn ranges.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
 virt/kvm/guest_memfd.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 5bf7c8b4509f..fea460e5e503 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -80,6 +80,21 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
 	return gfn - slot->base_gfn + slot->gmem.pgoff;
 }
 
+static gfn_t kvm_gmem_get_gfn(struct kvm_memory_slot *slot, pgoff_t pgoff)
+{
+	return slot->base_gfn + pgoff - slot->gmem.pgoff;
+}
+
+static gfn_t kvm_gmem_get_start_gfn(struct kvm_memory_slot *slot, pgoff_t start)
+{
+	return kvm_gmem_get_gfn(slot, max(slot->gmem.pgoff, start));
+}
+
+static gfn_t kvm_gmem_get_end_gfn(struct kvm_memory_slot *slot, pgoff_t end)
+{
+	return kvm_gmem_get_gfn(slot, min(slot->gmem.pgoff + slot->npages, end));
+}
+
 static u64 kvm_gmem_get_default_attributes(struct inode *inode)
 {
 	bool init_shared = GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED;
@@ -212,11 +227,9 @@ static void __kvm_gmem_invalidate_start(struct gmem_file *f, pgoff_t start,
 	unsigned long index;
 
 	xa_for_each_range(&f->bindings, index, slot, start, end - 1) {
-		pgoff_t pgoff = slot->gmem.pgoff;
-
 		struct kvm_gfn_range gfn_range = {
-			.start = slot->base_gfn + max(pgoff, start) - pgoff,
-			.end = slot->base_gfn + min(pgoff + slot->npages, end) - pgoff,
+			.start = kvm_gmem_get_start_gfn(slot, start),
+			.end = kvm_gmem_get_end_gfn(slot, end),
 			.slot = slot,
 			.may_block = true,
 			.attr_filter = attr_filter,
-- 
2.43.2