linux-kernel - [PATCH 1/1] arm64/entry.S: check for stack overflow in el1 case only

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Message-Id: <1607678131-20347-1-git-send-email-maninder1.s@samsung.com>
Date:   Fri, 11 Dec 2020 14:45:31 +0530
From:   Maninder Singh <maninder1.s@...sung.com>
To:     catalin.marinas@....com, will@...nel.org, mark.rutland@....com,
        broonie@...nel.org, vincenzo.frascino@....com,
        samitolvanen@...gle.com, ardb@...nel.org, maz@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        v.narang@...sung.com, a.sahrawat@...sung.com,
        Maninder Singh <maninder1.s@...sung.com>
Subject: [PATCH 1/1] arm64/entry.S: check for stack overflow in el1 case
 only

current code checks for sp bit flip in all exceptions,
but only el1 exceptions requires this. el0 can not enter
into stack overflow case directly.

it will improve performance for el0 exceptions and interrupts.

Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
Signed-off-by: Vaneet Narang <v.narang@...sung.com>
---
 arch/arm64/kernel/entry.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 2a93fa5..cad8faf 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -77,6 +77,7 @@ alternative_else_nop_endif
 
 	sub	sp, sp, #S_FRAME_SIZE
 #ifdef CONFIG_VMAP_STACK
+	.if	\el == 1
 	/*
 	 * Test whether the SP has overflowed, without corrupting a GPR.
 	 * Task and IRQ stacks are aligned so that SP & (1 << THREAD_SHIFT)
@@ -118,6 +119,7 @@ alternative_else_nop_endif
 	/* We were already on the overflow stack. Restore sp/x0 and carry on. */
 	sub	sp, sp, x0
 	mrs	x0, tpidrro_el0
+	.endif
 #endif
 	b	el\()\el\()_\label
 	.endm
-- 
1.9.1