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

[Qinglin Pan]

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. This patch 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.

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

Signed-off-by: Qinglin Pan <panqinglin2020 at iscas.ac.cn>
---
 arch/riscv/mm/init.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index c0cddf0fc22d..60a8e1dca79a 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -314,8 +314,18 @@ static void __init create_pte_mapping(pte_t *ptep,
 				      phys_addr_t sz, pgprot_t prot)
 {
 	uintptr_t pte_idx = pte_index(va);
-
-	BUG_ON(sz != PAGE_SIZE);
+	pte_t pte;
+
+	WARN_ON(sz != NAPOT_CONT64KB_SIZE && sz != PAGE_SIZE);
+	if (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;
+	}
 
 	if (pte_none(ptep[pte_idx]))
 		ptep[pte_idx] = pfn_pte(PFN_DOWN(pa), prot);
@@ -444,10 +454,13 @@ 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)))
-		return PAGE_SIZE;
+	if (!((base | size) & (PMD_SIZE - 1)))
+		return PMD_SIZE;
+
+	if (!((base | size) & (NAPOT_CONT64KB_SIZE - 1)))
+		return NAPOT_CONT64KB_SIZE;
 
-	return PMD_SIZE;
+	return PAGE_SIZE;
 }
 
 #ifdef CONFIG_XIP_KERNEL
-- 
2.32.0