[PATCH] arm64: Fix 5-level paging support in kexec/hibernate trampoline

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

Add the missing code to allocate P4D level page tables when cloning the
the kernel page tables. This fixes a crash that may be observed when
attempting to resume from hibernation on an LPA2 capable system with 4k
pages, which therefore uses 5 levels of paging.

Presumably, kexec is equally affected.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/mm/trans_pgd.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index 0f7b484cb2ff..84594f02f780 100644
--- a/arch/arm64/mm/trans_pgd.c
+++ b/arch/arm64/mm/trans_pgd.c
@@ -162,6 +162,13 @@ static int copy_p4d(struct trans_pgd_info *info, pgd_t *dst_pgdp,
 	unsigned long next;
 	unsigned long addr = start;
 
+	if (pgd_none(READ_ONCE(*dst_pgdp))) {
+		dst_p4dp = trans_alloc(info);
+		if (!dst_p4dp)
+			return -ENOMEM;
+		pgd_populate(NULL, dst_pgdp, dst_p4dp);
+	}
+
 	dst_p4dp = p4d_offset(dst_pgdp, start);
 	src_p4dp = p4d_offset(src_pgdp, start);
 	do {
-- 
2.47.1.688.g23fc6f90ad-goog