[PATCH 2/2] arm64: vmlinux.ld.S: add assertion for tramp_pg_dir offset

[Joey Gouly]

Add TRAMP_SWAPPER_OFFSET and use that instead of hardcoding
the offset between swapper_pg_dir and tramp_pg_dir.

Then use TRAMP_SWAPPER_OFFSET to assert that the offset is
correct at link time.

Signed-off-by: Joey Gouly <joey.gouly at arm.com>
---
 arch/arm64/include/asm/memory.h | 6 ++++++
 arch/arm64/kernel/entry.S       | 4 ++--
 arch/arm64/kernel/vmlinux.lds.S | 5 +++++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 300f728fa288..f9aa9fa8806e 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -165,6 +165,12 @@
  */
 #define RESERVED_SWAPPER_OFFSET	(PAGE_SIZE)
 
+/*
+ *  Open-coded (swapper_pg_dir - tramp_pg_dir) as this cannot be calculated
+ *  until link time.
+ */
+#define TRAMP_SWAPPER_OFFSET	(2 * PAGE_SIZE)
+
 #ifndef __ASSEMBLY__
 
 #include <linux/bitops.h>
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c9bae73f2621..c6aee646eb6b 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -805,7 +805,7 @@ SYM_CODE_END(ret_to_user)
 	// Move from tramp_pg_dir to swapper_pg_dir
 	.macro tramp_map_kernel, tmp
 	mrs	\tmp, ttbr1_el1
-	add	\tmp, \tmp, #(2 * PAGE_SIZE)
+	add	\tmp, \tmp, #TRAMP_SWAPPER_OFFSET
 	bic	\tmp, \tmp, #USER_ASID_FLAG
 	msr	ttbr1_el1, \tmp
 #ifdef CONFIG_QCOM_FALKOR_ERRATUM_1003
@@ -825,7 +825,7 @@ alternative_else_nop_endif
 	// Move from swapper_pg_dir to tramp_pg_dir
 	.macro tramp_unmap_kernel, tmp
 	mrs	\tmp, ttbr1_el1
-	sub	\tmp, \tmp, #(2 * PAGE_SIZE)
+	sub	\tmp, \tmp, #TRAMP_SWAPPER_OFFSET
 	orr	\tmp, \tmp, #USER_ASID_FLAG
 	msr	ttbr1_el1, \tmp
 	/*
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index a03a5300bce9..68f76a96c60b 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -319,3 +319,8 @@ ASSERT(_text == KIMAGE_VADDR, "HEAD is misaligned")
 
 ASSERT(swapper_pg_dir - reserved_pg_dir == RESERVED_SWAPPER_OFFSET,
        "RESERVED_SWAPPER_OFFSET is wrong!")
+
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+ASSERT(swapper_pg_dir - tramp_pg_dir == TRAMP_SWAPPER_OFFSET,
+       "TRAMP_SWAPPER_OFFSET is wrong!")
+#endif
-- 
2.17.1