Subject: [PATCH v7 1/9] arm64: Restrict undef hook for cpufeature registers

From: Rob Herring <[email-masked]>
Date: Mon, 19 Apr 2021 22:15:03 -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]>
---
v7:
 - Split off from Raphael's original undef hook patch as this change stands
   on its own.
---
 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 066030717a4c..aa0777690ab1 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2888,8 +2888,8 @@ 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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