[RFC PATCH 1/7] arm64: ptdump: Disregard unaddressable VA space

[Ard Biesheuvel]

Configurations built with support for 52-bit virtual addressing can also
run on CPUs that only support 48 bits of VA space, in which case only
that part of swapper_pg_dir that represents the 48-bit addressable
region is relevant, and everything else is ignored by the hardware.

In a future patch, we will clone the top 2 pgd_t entries at the bottom,
to support 52-bit VA configurations built for 16k pages and LPA2, where
we cannot simply point TTBR1 to the pgd_t entries where they actually
reside. However, we should avoid misinterpreting those cloned entries as
describing the start of the 52-bit VA space when the hardware does not
support that.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/mm/ptdump.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
index 9bc4066c5bf33a72..6c13bf6b7d5df4e4 100644
--- a/arch/arm64/mm/ptdump.c
+++ b/arch/arm64/mm/ptdump.c
@@ -358,7 +358,7 @@ void ptdump_check_wx(void)
 		.ptdump = {
 			.note_page = note_page,
 			.range = (struct ptdump_range[]) {
-				{PAGE_OFFSET, ~0UL},
+				{_PAGE_OFFSET(vabits_actual), ~0UL},
 				{0, 0}
 			}
 		}
@@ -380,6 +380,8 @@ static int __init ptdump_init(void)
 	address_markers[KASAN_START_NR].start_address = KASAN_SHADOW_START;
 #endif
 	ptdump_initialize();
+	if (VA_BITS > VA_BITS_MIN)
+		kernel_ptdump_info.base_addr = _PAGE_OFFSET(vabits_actual);
 	ptdump_debugfs_register(&kernel_ptdump_info, "kernel_page_tables");
 	return 0;
 }
-- 
2.35.1