linux-kernel - [PATCH 04/11] powerpc/64: Convert the syscall exit path to use RFI_TO

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Message-Id: <20180108165453.26066-4-mpe@ellerman.id.au>
Date:   Tue,  9 Jan 2018 03:54:46 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     linuxppc-dev@...abs.org
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, npiggin@...il.com, anton@...ba.org,
        mikey@...ling.org, oohall@...il.com, paulus@...ba.org
Subject: [PATCH 04/11] powerpc/64: Convert the syscall exit path to use RFI_TO_USER/KERNEL

From: Nicholas Piggin <npiggin@...il.com>

In the syscall exit path we may be returning to user or kernel
context. We already have a test for that, because we conditionally
restore r13. So use that existing test and branch, and bifurcate the
return based on that.

Signed-off-by: Nicholas Piggin <npiggin@...il.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
---
 arch/powerpc/kernel/entry_64.S | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 567d8f487f2f..b20c6cb0fa7f 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -267,13 +267,23 @@ BEGIN_FTR_SECTION
 END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 
 	ld	r13,GPR13(r1)	/* only restore r13 if returning to usermode */
+	ld	r2,GPR2(r1)
+	ld	r1,GPR1(r1)
+	mtlr	r4
+	mtcr	r5
+	mtspr	SPRN_SRR0,r7
+	mtspr	SPRN_SRR1,r8
+	RFI_TO_USER
+	b	.	/* prevent speculative execution */
+
+	/* exit to kernel */
 1:	ld	r2,GPR2(r1)
 	ld	r1,GPR1(r1)
 	mtlr	r4
 	mtcr	r5
 	mtspr	SPRN_SRR0,r7
 	mtspr	SPRN_SRR1,r8
-	RFI
+	RFI_TO_KERNEL
 	b	.	/* prevent speculative execution */
 
 .Lsyscall_error:
-- 
2.14.3