[PATCH v6 2/4] riscv: mm: support Svnapot in physical page linear-mapping

[panqinglin2020 at iscas.ac.cn]

From: Qinglin Pan <panqinglin2020 at iscas.ac.cn>

Svnapot is powerful when a physical region is going to mapped to a
virtual region. Kernel will do like this when mapping all allocable
physical pages to kernel vm space. Modify the create_pte_mapping
function used in linear-mapping procedure, so the kernel can be able
to use Svnapot when both address and length of physical region are
64KB align. Code here will be executed only when other size huge page
is not suitable, so it can be an addition of PMD_SIZE and PUD_SIZE mapping.

Modify the best_map_size function to give map_size many times instead
of only once, so a memory region can be mapped by both PMD_SIZE and
64KB napot size.

It is tested by setting qemu's memory to a 262272k region, and the
kernel can boot successfully.

Currently, the modified create_pte_mapping will never take use of SVNAPOT,
because this extension is detected and enabled in
riscv_fill_hwcap(called from setup_arch) which is called
after setup_vm_final. We will need to support function like
riscv_fill_hwcap_early to fill hardware capabilities more earlier, and
try to enable SVNAPOT more earlier in it, so that we can determine
SVNAPOT's presence when doing linear-mapping.

Signed-off-by: Qinglin Pan <panqinglin2020 at iscas.ac.cn>

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index b56a0a75533f..e6edc06b4543 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -373,9 +373,23 @@ static void __init create_pte_mapping(pte_t *ptep,
 				      phys_addr_t sz, pgprot_t prot)
 {
 	uintptr_t pte_idx = pte_index(va);
+	pte_t pte;
+
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_SVNAPOT))
+		goto normal_page;
+
+	if (has_svnapot() && sz == NAPOT_CONT64KB_SIZE) {
+		do {
+			pte = pfn_pte(PFN_DOWN(pa), prot);
+			ptep[pte_idx] = pte_mknapot(pte, NAPOT_CONT64KB_ORDER);
+			pte_idx++;
+			sz -= PAGE_SIZE;
+		} while (sz > 0);
+		return;
+	}
 
+normal_page:
 	BUG_ON(sz != PAGE_SIZE);
-
 	if (pte_none(ptep[pte_idx]))
 		ptep[pte_idx] = pfn_pte(PFN_DOWN(pa), prot);
 }
@@ -673,10 +687,18 @@ void __init create_pgd_mapping(pgd_t *pgdp,
 static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
 {
 	/* Upgrade to PMD_SIZE mappings whenever possible */
-	if ((base & (PMD_SIZE - 1)) || (size & (PMD_SIZE - 1)))
+	base &= PMD_SIZE - 1;
+	if (!base && size >= PMD_SIZE)
+		return PMD_SIZE;
+
+	if (!has_svnapot())
 		return PAGE_SIZE;
 
-	return PMD_SIZE;
+	base &= NAPOT_CONT64KB_SIZE - 1;
+	if (!base && size >= NAPOT_CONT64KB_SIZE)
+		return NAPOT_CONT64KB_SIZE;
+
+	return PAGE_SIZE;
 }
 
 #ifdef CONFIG_XIP_KERNEL
@@ -1111,9 +1133,9 @@ static void __init setup_vm_final(void)
 		if (end >= __pa(PAGE_OFFSET) + memory_limit)
 			end = __pa(PAGE_OFFSET) + memory_limit;
 
-		map_size = best_map_size(start, end - start);
 		for (pa = start; pa < end; pa += map_size) {
 			va = (uintptr_t)__va(pa);
+			map_size = best_map_size(pa, end - pa);
 
 			create_pgd_mapping(swapper_pg_dir, va, pa, map_size,
 					   pgprot_from_va(va));
-- 
2.35.1