riscv: Introduce huge page support for 32/64bit kernel

This patch implements both 4MB huge page support for 32bit kernel
and 2MB/1GB huge pages support for 64bit kernel.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>

2 files changed, 46 insertions, 0 deletions

diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index fc51d3b7876e..74055e1d6f21 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -12,3 +12,5 @@ obj-y += ioremap.o
 obj-y += cacheflush.o
 obj-y += context.o
 obj-y += sifive_l2_cache.o
+
+obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
diff --git a/arch/riscv/mm/hugetlbpage.c b/arch/riscv/mm/hugetlbpage.c
new file mode 100644
index 000000000000..0d4747e9d5b5
--- /dev/null
+++ b/arch/riscv/mm/hugetlbpage.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/hugetlb.h>
+#include <linux/err.h>
+
+int pud_huge(pud_t pud)
+{
+	return pud_present(pud) &&
+		(pud_val(pud) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
+}
+
+int pmd_huge(pmd_t pmd)
+{
+	return pmd_present(pmd) &&
+		(pmd_val(pmd) & (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC));
+}
+
+static __init int setup_hugepagesz(char *opt)
+{
+	unsigned long ps = memparse(opt, &opt);
+
+	if (ps == HPAGE_SIZE) {
+		hugetlb_add_hstate(HPAGE_SHIFT - PAGE_SHIFT);
+	} else if (IS_ENABLED(CONFIG_64BIT) && ps == PUD_SIZE) {
+		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
+	} else {
+		hugetlb_bad_size();
+		pr_err("hugepagesz: Unsupported page size %lu M\n", ps >> 20);
+		return 0;
+	}
+
+	return 1;
+}
+__setup("hugepagesz=", setup_hugepagesz);
+
+#ifdef CONFIG_CONTIG_ALLOC
+static __init int gigantic_pages_init(void)
+{
+	/* With CONTIG_ALLOC, we can allocate gigantic pages at runtime */
+	if (IS_ENABLED(CONFIG_64BIT) && !size_to_hstate(1UL << PUD_SHIFT))
+		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
+	return 0;
+}
+arch_initcall(gigantic_pages_init);
+#endif