[PATCH 4.2.y-ckt 040/268] arm64: kernel: enforce pmuserenr_el0 initialization and restore

From: Kamal Mostafa
Date: Wed Jan 27 2016 - 16:55:45 EST

4.2.8-ckt3 -stable review patch. If anyone has any objections, please let me know.


From: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>

commit 60792ad349f3c6dc5735aafefe5dc9121c79e320 upstream.

The pmuserenr_el0 register value is architecturally UNKNOWN on reset.
Current kernel code resets that register value iff the core pmu device is
correctly probed in the kernel. On platforms with missing DT pmu nodes (or
disabled perf events in the kernel), the pmu is not probed, therefore the
pmuserenr_el0 register is not reset in the kernel, which means that its
value retains the reset value that is architecturally UNKNOWN (system
may run with eg pmuserenr_el0 == 0x1, which means that PMU counters access
is available at EL0, which must be disallowed).

This patch adds code that resets pmuserenr_el0 on cold boot and restores
it on core resume from shutdown, so that the pmuserenr_el0 setup is
always enforced in the kernel.

Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
arch/arm64/kernel/perf_event.c | 3 ---
arch/arm64/mm/proc.S | 2 ++
2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index b31e9a4..b6c1301 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -1242,9 +1242,6 @@ static void armv8pmu_reset(void *info)

/* Initialize & Reset PMNC: C and P bits. */
armv8pmu_pmcr_write(ARMV8_PMCR_P | ARMV8_PMCR_C);
- /* Disable access from userspace. */
- asm volatile("msr pmuserenr_el0, %0" :: "r" (0));

static int armv8_pmuv3_map_event(struct perf_event *event)
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index f28a1fe..4730e39 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -119,6 +119,7 @@ ENTRY(cpu_do_resume)
ubfx x11, x11, #1, #1
msr oslar_el1, x11
+ msr pmuserenr_el0, xzr // Disable PMU access from EL0
mov x0, x12
dsb nsh // Make sure local tlb invalidation completed
@@ -158,6 +159,7 @@ ENTRY(__cpu_setup)
msr cpacr_el1, x0 // Enable FP/ASIMD
mov x0, #1 << 12 // Reset mdscr_el1 and disable
msr mdscr_el1, x0 // access to the DCC from EL0
+ msr pmuserenr_el0, xzr // Disable PMU access from EL0
* Memory region attributes for LPAE: