[PATCH v2 3/3] arm64: mm: set the contiguous bit for kernel mappings where appropriate

[Ard Biesheuvel]

Now that we no longer allow live kernel PMDs to be split, it is safe to
start using the contiguous bit for kernel mappings. So set the contiguous
bit in the kernel page mappings for regions whose size and alignment are
suitable for this. This includes contiguous level 2 mappings for 16k
granule kernels.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 arch/arm64/mm/mmu.c | 35 +++++++++++++++++---
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index ee3cda6c41a7..c2bf7396888b 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -102,8 +102,10 @@ static const pteval_t modifiable_attr_mask = PTE_PXN | PTE_RDONLY | PTE_WRITE;
 static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
 				  unsigned long end, unsigned long pfn,
 				  pgprot_t prot,
-				  phys_addr_t (*pgtable_alloc)(void))
+				  phys_addr_t (*pgtable_alloc)(void),
+				  bool page_mappings_only)
 {
+	pgprot_t __prot = prot;
 	pte_t *pte;
 
 	BUG_ON(pmd_sect(*pmd));
@@ -121,7 +123,18 @@ static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
 	do {
 		pte_t old_pte = *pte;
 
-		set_pte(pte, pfn_pte(pfn, prot));
+		/*
+		 * Set the contiguous bit for the subsequent group of PTEs if
+		 * its size and alignment are suitable.
+		 */
+		if (((addr | PFN_PHYS(pfn)) & ~CONT_PTE_MASK) == 0) {
+			if (!page_mappings_only && end - addr >= CONT_PTE_SIZE)
+				__prot = __pgprot(pgprot_val(prot) | PTE_CONT);
+			else
+				__prot = prot;
+		}
+
+		set_pte(pte, pfn_pte(pfn, __prot));
 		pfn++;
 
 		/*
@@ -141,6 +154,7 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
 				  phys_addr_t (*pgtable_alloc)(void),
 				  bool page_mappings_only)
 {
+	pgprot_t __prot = prot;
 	pmd_t *pmd;
 	unsigned long next;
 
@@ -164,10 +178,22 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
 
 		next = pmd_addr_end(addr, end);
 
+		/*
+		 * For 16K granule only, attempt to put down a 1 GB block by
+		 * stringing 32 PMD block mappings together.
+		 */
+		if (IS_ENABLED(CONFIG_ARM64_16K_PAGES) &&
+		    ((addr | phys) & ~CONT_PMD_MASK) == 0) {
+			if (!page_mappings_only && end - addr >= CONT_PMD_SIZE)
+				__prot = __pgprot(pgprot_val(prot) | PTE_CONT);
+			else
+				__prot = prot;
+		}
+
 		/* try section mapping first */
 		if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
 		      !page_mappings_only) {
-			pmd_set_huge(pmd, phys, prot);
+			pmd_set_huge(pmd, phys, __prot);
 
 			/*
 			 * After the PMD entry has been populated once, we
@@ -178,7 +204,8 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
 				~modifiable_attr_mask) != 0);
 		} else {
 			alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
-				       prot, pgtable_alloc);
+				       prot, pgtable_alloc,
+				       page_mappings_only);
 
 			BUG_ON(!pmd_none(old_pmd) &&
 			       pmd_val(old_pmd) != pmd_val(*pmd));
-- 
2.7.4