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Date:   Thu,  5 Jan 2023 10:18:30 +0000
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Message-ID: <20230105101844.1893104-33-jthoughton@google.com>
Subject: [PATCH 32/46] hugetlb: add for_each_hgm_shift
From:   James Houghton <jthoughton@google.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Peter Xu <peterx@redhat.com>
Cc:     David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        "Zach O'Keefe" <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        James Houghton <jthoughton@google.com>
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Precedence: bulk

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@google.com>
---
 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