[PATCH] arm64: trans_pgd: clone only the linear map that exists at runtime

[Breno Leitao]

kexec_file_load() fails on arm64 if we have CONFIG_ARM64_VA_BITS_52 but
it runs on a !FEAT_LPA2 host (such as my loving Grace machine).

That is because trans_pgd_create_copy() uses the compile time
PAGE_OFFSET (VA 52) instead of the actual VA size (48 -- due to the lack
of LPA2). With the fifth level folded, pgd_none() is always false, so
the walk cannot skip the 15 extra PGDIR_SIZE slots, and they all alias
back to the same table: the whole kernel page table gets cloned 16
times, KASAN shadow included. Without KASAN it does not blow up, it just
wastes ~RAM/32 in page tables.

Fix it by copying the linear map that is the actual one, not the
compiled one.

Fixes: a6bbf5d4d9d1 ("arm64: mm: Add definitions to support 5 levels of paging")
Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
 arch/arm64/kernel/machine_kexec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index c5693a32e49b0..8f9bc2327dc85 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -129,7 +129,8 @@ int machine_kexec_post_load(struct kimage *kimage)
 	}
 
 	/* Create a copy of the linear map */
-	rc = trans_pgd_create_copy(&info, &trans_pgd, PAGE_OFFSET, PAGE_END);
+	rc = trans_pgd_create_copy(&info, &trans_pgd,
+				   _PAGE_OFFSET(vabits_actual), PAGE_END);
 	if (rc)
 		return rc;
 	kimage->arch.ttbr1 = __pa(trans_pgd);

---
base-commit: b8809969e1d7a591e0f49dd464a5d04b3cf02ab1
change-id: 20260826-b4-arm64-trans-pgd-va52-0bb9b44dd896

Best regards,
--  
Breno Leitao <leitao@xxxxxxxxxx>