[PATCH 32/46] hugetlb: add for_each_hgm_shift

[James Houghton]

This is a helper macro to loop through all the usable page sizes for a
high-granularity-enabled HugeTLB VMA. Given the VMA's hstate, it will
loop, in descending order, through the page sizes that HugeTLB supports
for this architecture. It always includes PAGE_SIZE.

This is done by looping through the hstates; however, there is no
hstate for PAGE_SIZE. To handle this case, the loop intentionally goes
out of bounds, and the out-of-bounds pointer is mapped to PAGE_SIZE.

Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
 mm/hugetlb.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1e9e149587b3..1eef6968b1fa 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -7780,6 +7780,24 @@ bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
 {
 	return vma && (vma->vm_flags & VM_HUGETLB_HGM);
 }
+/* Should only be used by the for_each_hgm_shift macro. */
+static unsigned int __shift_for_hstate(struct hstate *h)
+{
+	/* If h is out of bounds, we have reached the end, so give PAGE_SIZE */
+	if (h >= &hstates[hugetlb_max_hstate])
+		return PAGE_SHIFT;
+	return huge_page_shift(h);
+}
+
+/*
+ * Intentionally go out of bounds. An out-of-bounds hstate will be converted to
+ * PAGE_SIZE.
+ */
+#define for_each_hgm_shift(hstate, tmp_h, shift) \
+	for ((tmp_h) = hstate; (shift) = __shift_for_hstate(tmp_h), \
+			       (tmp_h) <= &hstates[hugetlb_max_hstate]; \
+			       (tmp_h)++)
+
 #endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
 
 /*
-- 
2.39.0.314.g84b9a713c41-goog