[PATCH] arm64/kernel/entry: refine comment of stack overflow check

[Heyi Guo]

Stack overflow checking can be done by testing
sp & (1 << THREAD_SHIFT)
only for the stacks are aligned to (2 << THREAD_SHIFT) with size of
(1 << THREAD_SIZE), and this is the case when CONFIG_VMAP_STACK is
set.

Fix the code comment to avoid confusion.

Signed-off-by: Heyi Guo <guoheyi@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
---
 arch/arm64/kernel/entry.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index cf3bd2976e57..9e8ba507090f 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -76,7 +76,8 @@ alternative_else_nop_endif
 #ifdef CONFIG_VMAP_STACK
 	/*
 	 * Test whether the SP has overflowed, without corrupting a GPR.
-	 * Task and IRQ stacks are aligned to (1 << THREAD_SHIFT).
+	 * Task and IRQ stacks are aligned to (2 << THREAD_SHIFT) with size of
+	 * (1 << THREAD_SHIFT).
 	 */
 	add	sp, sp, x0			// sp' = sp + x0
 	sub	x0, sp, x0			// x0' = sp' - x0 = (sp + x0) - x0 = sp
-- 
2.19.1