[PATCH v1 3/3] KVM: s390: Allow for 2G hugepages

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

Change gmap_2g_allowed() to perform the necessary checks to allow for
2G hugepages to be used, instead of returning false. The
GMAP_FLAG_ALLOW_HPAGE_2G gmap flag is now taken into account.

Also add appropriate kerneldoc comments.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/gmap.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index c9e348149ba1..c5a8132eaa22 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -635,10 +635,27 @@ int gmap_try_fixup_minor(struct gmap *gmap, struct guest_fault *fault)
 	return rc;
 }
 
+/**
+ * gmap_2g_allowed() - Check whether a 2G hugepage is allowed.
+ * @gmap: The gmap of the guest.
+ * @f: Describes the fault that is being resolved.
+ * @slot: The memslot the faulting address belongs to.
+ *
+ * The function checks whether the GMAP_FLAG_ALLOW_HPAGE_2G flag is set for
+ * @gmap, whether the offset of the address in the 2G virtual frame is the
+ * same as the offset in the physical 2G frame, and finally whether the whole
+ * 2G page would fit in the given memslot.
+ *
+ * Return: true if a 2G hugepage is allowed to back the faulting address, false
+ *         otherwise.
+ */
 static inline bool gmap_2g_allowed(struct gmap *gmap, struct guest_fault *f,
 				   struct kvm_memory_slot *slot)
 {
-	return false;
+	return test_bit(GMAP_FLAG_ALLOW_HPAGE_2G, &gmap->flags) &&
+	       !((f->gfn ^ f->pfn) & ~_REGION3_FR_MASK) &&
+	       slot->base_gfn <= ALIGN_DOWN(f->gfn, _PAGES_PER_REGION3) &&
+	       slot->base_gfn + slot->npages >= ALIGN(f->gfn + 1, _PAGES_PER_REGION3);
 }
 
 /**
-- 
2.54.0