Subject: [PATCH v2] arm64: Restrict undef hook for cpufeature registers

From: Rob Herring <[email-masked]>
Date: Mon, 17 May 2021 13:02:56 -0500

From: Raphael Gault <[email-masked]>

This commit modifies the mask of the mrs_hook declared in
arch/arm64/kernel/cpufeatures.c which emulates only feature register
access. This is necessary because this hook's mask was too large and
thus masking any mrs instruction, even if not related to the emulated
registers which made the pmu emulation inefficient.

Signed-off-by: Raphael Gault <[email-masked]>
Signed-off-by: Rob Herring <[email-masked]>
---
I don't *think* I'm going to need this for the perf userspace counter 
access, but this patch stands on its own as the PMU registers are not 
emulated. So please apply it.

v2:
 - Fix warning for set but unused sys_reg
---
 arch/arm64/kernel/cpufeature.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index efed2830d141..c773f7c3c007 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2905,8 +2905,8 @@ static int emulate_mrs(struct pt_regs *regs, u32 insn)
 }
 
 static struct undef_hook mrs_hook = {
-	.instr_mask = 0xfff00000,
-	.instr_val  = 0xd5300000,
+	.instr_mask = 0xffff0000,
+	.instr_val  = 0xd5380000,
 	.pstate_mask = PSR_AA32_MODE_MASK,
 	.pstate_val = PSR_MODE_EL0t,
 	.fn = emulate_mrs,
-- 
2.27.0

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