powerpc/8xx: Support 16k hugepages with 4k pages

The 8xx has 4 page sizes: 4k, 16k, 512k and 8M

4k and 16k can be selected at build time as standard page sizes,
and 512k and 8M are hugepages.

When 4k standard pages are selected, 16k pages are not available.

Allow 16k pages as hugepages when 4k pages are used.

To allow that, implement arch_make_huge_pte() which receives
the necessary arguments to allow setting the PTE in accordance
with the page size:
- 512 k pages must have _PAGE_HUGE and _PAGE_SPS. They are set
by pte_mkhuge(). arch_make_huge_pte() does nothing.
- 16 k pages must have only _PAGE_SPS. arch_make_huge_pte() clears
_PAGE_HUGE.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a518abc29266a708dfbccc8fce9ae6694fe4c2c6.1598862623.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h

@@ -65,4 +65,18 @@ static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
 	pte_update(mm, addr, ptep, clr, set, 1);
 }
 
+#ifdef CONFIG_PPC_4K_PAGES
+static inline pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
+				       struct page *page, int writable)
+{
+	size_t size = huge_page_size(hstate_vma(vma));
+
+	if (size == SZ_16K)
+		return __pte(pte_val(entry) & ~_PAGE_HUGE);
+	else
+		return entry;
+}
+#define arch_make_huge_pte arch_make_huge_pte
+#endif
+
 #endif /* _ASM_POWERPC_NOHASH_32_HUGETLB_8XX_H */

arch/powerpc/include/asm/nohash/32/pgtable.h

@@ -235,6 +235,8 @@ static int number_of_cells_per_pte(pmd_t *pmd, pte_basic_t val, int huge)
 		return PAGE_SIZE / SZ_4K;
 	else if (hugepd_ok(*((hugepd_t *)pmd)))
 		return 1;
+	else if (IS_ENABLED(CONFIG_PPC_4K_PAGES) && !(val & _PAGE_HUGE))
+		return SZ_16K / SZ_4K;
 	else
 		return SZ_512K / SZ_4K;
 }

arch/powerpc/mm/hugetlbpage.c

@@ -180,7 +180,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz
 	if (!hpdp)
 		return NULL;
 
-	if (IS_ENABLED(CONFIG_PPC_8xx) && sz == SZ_512K)
+	if (IS_ENABLED(CONFIG_PPC_8xx) && pshift < PMD_SHIFT)
 		return pte_alloc_map(mm, (pmd_t *)hpdp, addr);
 
 	BUG_ON(!hugepd_none(*hpdp) && !hugepd_ok(*hpdp));

arch/powerpc/mm/nohash/tlb.c

@@ -83,16 +83,12 @@ struct mmu_psize_def mmu_psize_defs[MMU_PAGE_COUNT] = {
 };
 #elif defined(CONFIG_PPC_8xx)
 struct mmu_psize_def mmu_psize_defs[MMU_PAGE_COUNT] = {
-	/* we only manage 4k and 16k pages as normal pages */
-#ifdef CONFIG_PPC_4K_PAGES
 	[MMU_PAGE_4K] = {
 		.shift	= 12,
 	},
-#else
 	[MMU_PAGE_16K] = {
 		.shift	= 14,
 	},
-#endif
 	[MMU_PAGE_512K] = {
 		.shift	= 19,
 	},

arch/powerpc/mm/ptdump/8xx.c

@@ -11,8 +11,13 @@
 
 static const struct flag_info flag_array[] = {
 	{
+#ifdef CONFIG_PPC_16K_PAGES
 		.mask	= _PAGE_HUGE,
 		.val	= _PAGE_HUGE,
+#else
+		.mask	= _PAGE_SPS,
+		.val	= _PAGE_SPS,
+#endif
 		.set	= "huge",
 		.clear	= "    ",
 	}, {

include/uapi/asm-generic/hugetlb_encode.h

@@ -20,6 +20,7 @@
 #define HUGETLB_FLAG_ENCODE_SHIFT	26
 #define HUGETLB_FLAG_ENCODE_MASK	0x3f
 
+#define HUGETLB_FLAG_ENCODE_16KB	(14 << HUGETLB_FLAG_ENCODE_SHIFT)
 #define HUGETLB_FLAG_ENCODE_64KB	(16 << HUGETLB_FLAG_ENCODE_SHIFT)
 #define HUGETLB_FLAG_ENCODE_512KB	(19 << HUGETLB_FLAG_ENCODE_SHIFT)
 #define HUGETLB_FLAG_ENCODE_1MB		(20 << HUGETLB_FLAG_ENCODE_SHIFT)

include/uapi/linux/mman.h

@@ -27,6 +27,7 @@
 #define MAP_HUGE_SHIFT	HUGETLB_FLAG_ENCODE_SHIFT
 #define MAP_HUGE_MASK	HUGETLB_FLAG_ENCODE_MASK
 
+#define MAP_HUGE_16KB	HUGETLB_FLAG_ENCODE_16KB
 #define MAP_HUGE_64KB	HUGETLB_FLAG_ENCODE_64KB
 #define MAP_HUGE_512KB	HUGETLB_FLAG_ENCODE_512KB
 #define MAP_HUGE_1MB	HUGETLB_FLAG_ENCODE_1MB