linux-kernel - [PATCH] arm64: perf: Ensure EL0 access is disabled at reset

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Date:   Tue, 27 Apr 2021 08:48:52 -0500
From:   Rob Herring <robh@...nel.org>
To:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: [PATCH] arm64: perf: Ensure EL0 access is disabled at reset

The ER, SW, and EN bits in the PMUSERENR_EL0 register are UNKNOWN at
reset and the register is never initialized, so EL0 access could be
enabled by default on some implementations. Let's initialize
PMUSERENR_EL0 to a known state with EL0 access disabled.

Signed-off-by: Rob Herring <robh@...nel.org>
---
 arch/arm64/kernel/perf_event.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 4658fcf88c2b..c32778ae5117 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -450,6 +450,11 @@ static inline void armv8pmu_pmcr_write(u32 val)
 	write_sysreg(val, pmcr_el0);
 }
 
+static void armv8pmu_clear_pmuserenr(void)
+{
+	write_sysreg(0, pmuserenr_el0);
+}
+
 static inline int armv8pmu_has_overflowed(u32 pmovsr)
 {
 	return pmovsr & ARMV8_PMU_OVERFLOWED_MASK;
@@ -933,6 +938,9 @@ static void armv8pmu_reset(void *info)
 	armv8pmu_disable_counter(U32_MAX);
 	armv8pmu_disable_intens(U32_MAX);
 
+	/* User access is unknown at reset. */
+	armv8pmu_clear_pmuserenr();
+
 	/* Clear the counters we flip at guest entry/exit */
 	kvm_clr_pmu_events(U32_MAX);
 
-- 
2.27.0