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From: Mark Rutland <mark.rutland@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: catalin.marinas@arm.com, james.morse@arm.com,
	mark.rutland@arm.com, robh@kernel.org, stable@vger.kernel.org,
	will@kernel.org
Subject: [PATCH 2/2] arm64: entry: simplify kernel_exit logic
Date: Tue, 16 Jan 2024 11:02:21 +0000	[thread overview]
Message-ID: <20240116110221.420467-3-mark.rutland@arm.com> (raw)
In-Reply-To: <20240116110221.420467-1-mark.rutland@arm.com>

For historical reasons, the non-KPTI exception return path is duplicated for
EL1 and EL0, with the structure:

	.if \el == 0
	[ KPTI handling ]
	ldr     lr, [sp, #S_LR]
 	add	sp, sp, #PT_REGS_SIZE		// restore sp
	[ EL0 exception return workaround ]
	eret
	.else
	ldr     lr, [sp, #S_LR]
 	add	sp, sp, #PT_REGS_SIZE		// restore sp
	[ EL1 exception return workaround ]
	eret
	.endif
	sb

This would be simpler and clearer with the common portions factored out,
e.g.

	.if \el == 0
	[ KPTI handling ]
	.endif

	ldr     lr, [sp, #S_LR]
 	add	sp, sp, #PT_REGS_SIZE		// restore sp

	.if \el == 0
	[ EL0 exception return workaround ]
	.else
	[ EL1 exception return workaround ]
	.endif

	eret
	sb

This expands to the same code, but is simpler for a human to follow as
it avoids duplicates the restore of LR+SP, and makes it clear that the
ERET is associated with the SB.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/entry.S | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 7fcbee0f6c0e4..7ef0e127b149f 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -442,24 +442,23 @@ alternative_else_nop_endif
 
 .L_skip_tramp_exit_\@:
 #endif
+	.endif
+
 	ldr	lr, [sp, #S_LR]
 	add	sp, sp, #PT_REGS_SIZE		// restore sp
 
+	.if \el == 0
 	/* This must be after the last explicit memory access */
 alternative_if ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD
 	tlbi	vale1, xzr
 	dsb	nsh
 alternative_else_nop_endif
-	eret
 	.else
-	ldr	lr, [sp, #S_LR]
-	add	sp, sp, #PT_REGS_SIZE		// restore sp
-
 	/* Ensure any device/NC reads complete */
 	alternative_insn nop, "dmb sy", ARM64_WORKAROUND_1508412
+	.endif
 
 	eret
-	.endif
 	sb
 	.endm
 
-- 
2.30.2


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  parent reply	other threads:[~2024-01-16 11:03 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-01-16 11:02 [PATCH 0/2] arm64: fix+cleanup for ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD Mark Rutland
2024-01-16 11:02 ` [PATCH 1/2] arm64: entry: fix ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD Mark Rutland
2024-01-19 15:11   ` Rob Herring
2024-01-22 11:16     ` Mark Rutland
2024-01-16 11:02 ` Mark Rutland [this message]
2024-01-18 12:02 ` [PATCH 0/2] arm64: fix+cleanup for ARM64_WORKAROUND_SPECULATIVE_UNPRIV_LOAD Will Deacon
2024-01-19 10:32   ` Mark Rutland

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