[PATCH 5/6] arm64: use HW PTE accessors in early map_range()

[Muhammad Usama Anjum <usama.anjum@arm.com>]

map_range() uses HW PTE pointers to build early translation tables at
each level. Directly testing, decoding, or assigning *tbl treats an
HW PTE as a SW PTE value, which requires explicit conversion once
hw_pte_t becomes distinct.

Use __ptep_get() to load a SW PTE value for the empty-entry check and
child-table address, and __set_pte_nosync() to convert SW PTE values to
HW PTEs on stores. The no-sync helper performs WRITE_ONCE() without
adding the completion barriers used by __set_pte().

Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
---
 arch/arm64/kernel/pi/map_range.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/pi/map_range.c b/arch/arm64/kernel/pi/map_range.c
index 94f06da76e333..9c4c8060c5df4 100644
--- a/arch/arm64/kernel/pi/map_range.c
+++ b/arch/arm64/kernel/pi/map_range.c
@@ -51,19 +51,21 @@ void __init map_range(phys_addr_t *pte, u64 start, u64 end, phys_addr_t pa,
 
 	while (start < end) {
 		u64 next = min((start | lmask) + 1, PAGE_ALIGN(end));
+		pte_t entry = __ptep_get(tbl);
 
 		if (level < 2 || (level == 2 && (start | next | pa) & lmask)) {
 			/*
 			 * This chunk needs a finer grained mapping. Create a
 			 * table mapping if necessary and recurse.
 			 */
-			if (pte_none(*tbl)) {
-				*tbl = __pte(__phys_to_pte_val(*pte) |
+			if (pte_none(entry)) {
+				entry = __pte(__phys_to_pte_val(*pte) |
 					     PMD_TYPE_TABLE | PMD_TABLE_UXN);
-				*pte += PTRS_PER_PTE * sizeof(pte_t);
+				__set_pte_nosync(tbl, entry);
+				*pte += PTRS_PER_PTE * sizeof(hw_pte_t);
 			}
 			map_range(pte, start, next, pa, prot, level + 1,
-				  (hw_pte_t *)(__pte_to_phys(*tbl) + va_offset),
+				  (hw_pte_t *)(__pte_to_phys(entry) + va_offset),
 				  may_use_cont, va_offset);
 		} else {
 			/*
@@ -81,7 +83,8 @@ void __init map_range(phys_addr_t *pte, u64 start, u64 end, phys_addr_t pa,
 				protval &= ~PTE_CONT;
 
 			/* Put down a block or page mapping */
-			*tbl = __pte(__phys_to_pte_val(pa) | protval);
+			entry = __pte(__phys_to_pte_val(pa) | protval);
+			__set_pte_nosync(tbl, entry);
 		}
 		pa += next - start;
 		start = next;

-- 
2.47.3