If the PMU is partitioned, keep the driver out of the guest counter
partition and only use the host counter partition. Partitioning is
defined by the MDCR_EL2.HPMN register field and saved in
cpu_pmu->hpmn. The range 0..HPMN-1 is accessible by EL1 and EL0 while
HPMN..PMCR.N is reserved for EL2.

Define some macros that take HPMN as an argument and construct
mutually exclusive bitmaps for testing which partition a particular
counter is in. Note that despite their different position in the
bitmap, the cycle and instruction counters are always in the guest
partition.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
 arch/arm/include/asm/arm_pmuv3.h |  2 +
 arch/arm64/include/asm/kvm_pmu.h |  5 +++
 arch/arm64/kvm/pmu-part.c        | 16 +++++++
 drivers/perf/arm_pmuv3.c         | 73 +++++++++++++++++++++++++++-----
 include/linux/perf/arm_pmuv3.h   |  8 ++++
 5 files changed, 94 insertions(+), 10 deletions(-)

diff --git a/arch/arm/include/asm/arm_pmuv3.h b/arch/arm/include/asm/arm_pmuv3.h
index 2ec0e5e83fc9..dadd4ddf51af 100644
--- a/arch/arm/include/asm/arm_pmuv3.h
+++ b/arch/arm/include/asm/arm_pmuv3.h
@@ -227,6 +227,8 @@ static inline bool kvm_set_pmuserenr(u64 val)
 }
 
 static inline void kvm_vcpu_pmu_resync_el0(void) {}
+static inline void kvm_pmu_host_counters_enable(void) {}
+static inline void kvm_pmu_host_counters_disable(void) {}
 
 /* PMU Version in DFR Register */
 #define ARMV8_PMU_DFR_VER_NI        0
diff --git a/arch/arm64/include/asm/kvm_pmu.h b/arch/arm64/include/asm/kvm_pmu.h
index 174b7f376d95..8f25754fde47 100644
--- a/arch/arm64/include/asm/kvm_pmu.h
+++ b/arch/arm64/include/asm/kvm_pmu.h
@@ -25,6 +25,8 @@ void kvm_host_pmu_init(struct arm_pmu *pmu);
 u8 kvm_pmu_get_reserved_counters(void);
 u8 kvm_pmu_hpmn(u8 nr_counters);
 void kvm_pmu_partition(struct arm_pmu *pmu);
+void kvm_pmu_host_counters_enable(void);
+void kvm_pmu_host_counters_disable(void);
 
 #else
 
@@ -37,6 +39,9 @@ static inline bool kvm_set_pmuserenr(u64 val)
 static inline void kvm_vcpu_pmu_resync_el0(void) {}
 static inline void kvm_host_pmu_init(struct arm_pmu *pmu) {}
 
+static inline void kvm_pmu_host_counters_enable(void) {}
+static inline void kvm_pmu_host_counters_disable(void) {}
+
 #endif
 
 #endif
diff --git a/arch/arm64/kvm/pmu-part.c b/arch/arm64/kvm/pmu-part.c
index e74fecc67e37..51da65c678f9 100644
--- a/arch/arm64/kvm/pmu-part.c
+++ b/arch/arm64/kvm/pmu-part.c
@@ -45,3 +45,19 @@ void kvm_pmu_partition(struct arm_pmu *pmu)
 		pmu->partitioned = false;
 	}
 }
+
+void kvm_pmu_host_counters_enable(void)
+{
+	u64 mdcr = read_sysreg(mdcr_el2);
+
+	mdcr |= MDCR_EL2_HPME;
+	write_sysreg(mdcr, mdcr_el2);
+}
+
+void kvm_pmu_host_counters_disable(void)
+{
+	u64 mdcr = read_sysreg(mdcr_el2);
+
+	mdcr &= ~MDCR_EL2_HPME;
+	write_sysreg(mdcr, mdcr_el2);
+}
diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index 0e360feb3432..442dcff56d5b 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -730,15 +730,19 @@ static void armv8pmu_disable_event_irq(struct perf_event *event)
 	armv8pmu_disable_intens(BIT(event->hw.idx));
 }
 
-static u64 armv8pmu_getreset_flags(void)
+static u64 armv8pmu_getreset_flags(struct arm_pmu *cpu_pmu)
 {
 	u64 value;
 
 	/* Read */
 	value = read_pmovsclr();
 
+	if (cpu_pmu->partitioned)
+		value &= ARMV8_PMU_HOST_CNT_PART(cpu_pmu->hpmn);
+	else
+		value &= ARMV8_PMU_OVERFLOWED_MASK;
+
 	/* Write to clear flags */
-	value &= ARMV8_PMU_OVERFLOWED_MASK;
 	write_pmovsclr(value);
 
 	return value;
@@ -765,6 +769,18 @@ static void armv8pmu_disable_user_access(void)
 	update_pmuserenr(0);
 }
 
+static bool armv8pmu_is_guest_part(struct arm_pmu *cpu_pmu, u8 idx)
+{
+	return cpu_pmu->partitioned &&
+		(BIT(idx) & ARMV8_PMU_GUEST_CNT_PART(cpu_pmu->hpmn));
+}
+
+static bool armv8pmu_is_host_part(struct arm_pmu *cpu_pmu, u8 idx)
+{
+	return !cpu_pmu->partitioned ||
+		(BIT(idx) & ARMV8_PMU_HOST_CNT_PART(cpu_pmu->hpmn));
+}
+
 static void armv8pmu_enable_user_access(struct arm_pmu *cpu_pmu)
 {
 	int i;
@@ -773,6 +789,8 @@ static void armv8pmu_enable_user_access(struct arm_pmu *cpu_pmu)
 	if (is_pmuv3p9(cpu_pmu->pmuver)) {
 		u64 mask = 0;
 		for_each_set_bit(i, cpuc->used_mask, ARMPMU_MAX_HWEVENTS) {
+			if (armv8pmu_is_guest_part(cpu_pmu, i))
+				continue;
 			if (armv8pmu_event_has_user_read(cpuc->events[i]))
 				mask |= BIT(i);
 		}
@@ -781,6 +799,8 @@ static void armv8pmu_enable_user_access(struct arm_pmu *cpu_pmu)
 		/* Clear any unused counters to avoid leaking their contents */
 		for_each_andnot_bit(i, cpu_pmu->cntr_mask, cpuc->used_mask,
 				    ARMPMU_MAX_HWEVENTS) {
+			if (armv8pmu_is_guest_part(cpu_pmu, i))
+				continue;
 			if (i == ARMV8_PMU_CYCLE_IDX)
 				write_pmccntr(0);
 			else if (i == ARMV8_PMU_INSTR_IDX)
@@ -825,8 +845,10 @@ static void armv8pmu_start(struct arm_pmu *cpu_pmu)
 	else
 		armv8pmu_disable_user_access();
 
-	/* Enable all counters */
-	armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
+	if (cpu_pmu->partitioned)
+		kvm_pmu_host_counters_enable();
+	else
+		armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
 
 	kvm_vcpu_pmu_resync_el0();
 }
@@ -834,7 +856,10 @@ static void armv8pmu_start(struct arm_pmu *cpu_pmu)
 static void armv8pmu_stop(struct arm_pmu *cpu_pmu)
 {
 	/* Disable all counters */
-	armv8pmu_pmcr_write(armv8pmu_pmcr_read() & ~ARMV8_PMU_PMCR_E);
+	if (cpu_pmu->partitioned)
+		kvm_pmu_host_counters_disable();
+	else
+		armv8pmu_pmcr_write(armv8pmu_pmcr_read() & ~ARMV8_PMU_PMCR_E);
 }
 
 static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
@@ -848,7 +873,7 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
 	/*
 	 * Get and reset the IRQ flags
 	 */
-	pmovsr = armv8pmu_getreset_flags();
+	pmovsr = armv8pmu_getreset_flags(cpu_pmu);
 
 	/*
 	 * Did an overflow occur?
@@ -906,6 +931,8 @@ static int armv8pmu_get_single_idx(struct pmu_hw_events *cpuc,
 	int idx;
 
 	for_each_set_bit(idx, cpu_pmu->cntr_mask, ARMV8_PMU_MAX_GENERAL_COUNTERS) {
+		if (armv8pmu_is_guest_part(cpu_pmu, idx))
+			continue;
 		if (!test_and_set_bit(idx, cpuc->used_mask))
 			return idx;
 	}
@@ -922,6 +949,8 @@ static int armv8pmu_get_chain_idx(struct pmu_hw_events *cpuc,
 	 * the lower idx must be even.
 	 */
 	for_each_set_bit(idx, cpu_pmu->cntr_mask, ARMV8_PMU_MAX_GENERAL_COUNTERS) {
+		if (armv8pmu_is_guest_part(cpu_pmu, idx))
+			continue;
 		if (!(idx & 0x1))
 			continue;
 		if (!test_and_set_bit(idx, cpuc->used_mask)) {
@@ -944,6 +973,7 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 
 	/* Always prefer to place a cycle counter into the cycle counter. */
 	if ((evtype == ARMV8_PMUV3_PERFCTR_CPU_CYCLES) &&
+	    !cpu_pmu->partitioned &&
 	    !armv8pmu_event_get_threshold(&event->attr)) {
 		if (!test_and_set_bit(ARMV8_PMU_CYCLE_IDX, cpuc->used_mask))
 			return ARMV8_PMU_CYCLE_IDX;
@@ -959,6 +989,7 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 	 * may not know how to handle it.
 	 */
 	if ((evtype == ARMV8_PMUV3_PERFCTR_INST_RETIRED) &&
+	    !cpu_pmu->partitioned &&
 	    !armv8pmu_event_get_threshold(&event->attr) &&
 	    test_bit(ARMV8_PMU_INSTR_IDX, cpu_pmu->cntr_mask) &&
 	    !armv8pmu_event_want_user_access(event)) {
@@ -970,7 +1001,7 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc,
 	 * Otherwise use events counters
 	 */
 	if (armv8pmu_event_is_chained(event))
-		return	armv8pmu_get_chain_idx(cpuc, cpu_pmu);
+		return armv8pmu_get_chain_idx(cpuc, cpu_pmu);
 	else
 		return armv8pmu_get_single_idx(cpuc, cpu_pmu);
 }
@@ -1062,6 +1093,16 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event,
 	return 0;
 }
 
+static void armv8pmu_reset_host_counters(struct arm_pmu *cpu_pmu)
+{
+	int idx;
+
+	for_each_set_bit(idx, cpu_pmu->cntr_mask, ARMV8_PMU_MAX_GENERAL_COUNTERS) {
+		if (armv8pmu_is_host_part(cpu_pmu, idx))
+			armv8pmu_write_evcntr(idx, 0);
+	}
+}
+
 static void armv8pmu_reset(void *info)
 {
 	struct arm_pmu *cpu_pmu = (struct arm_pmu *)info;
@@ -1069,6 +1110,9 @@ static void armv8pmu_reset(void *info)
 
 	bitmap_to_arr64(&mask, cpu_pmu->cntr_mask, ARMPMU_MAX_HWEVENTS);
 
+	if (cpu_pmu->partitioned)
+		mask &= ARMV8_PMU_HOST_CNT_PART(cpu_pmu->hpmn);
+
 	/* The counter and interrupt enable registers are unknown at reset. */
 	armv8pmu_disable_counter(mask);
 	armv8pmu_disable_intens(mask);
@@ -1076,11 +1120,20 @@ static void armv8pmu_reset(void *info)
 	/* Clear the counters we flip at guest entry/exit */
 	kvm_clr_pmu_events(mask);
 
+
+	pmcr = ARMV8_PMU_PMCR_LC;
+
 	/*
-	 * Initialize & Reset PMNC. Request overflow interrupt for
-	 * 64 bit cycle counter but cheat in armv8pmu_write_counter().
+	 * Initialize & Reset PMNC. Request overflow interrupt for 64
+	 * bit cycle counter but cheat in armv8pmu_write_counter().
+	 *
+	 * When partitioned, there is no single bit to reset only the
+	 * host counters. so reset them individually.
 	 */
-	pmcr = ARMV8_PMU_PMCR_P | ARMV8_PMU_PMCR_C | ARMV8_PMU_PMCR_LC;
+	if (cpu_pmu->partitioned)
+		armv8pmu_reset_host_counters(cpu_pmu);
+	else
+		pmcr = ARMV8_PMU_PMCR_P | ARMV8_PMU_PMCR_C;
 
 	/* Enable long event counter support where available */
 	if (armv8pmu_has_long_event(cpu_pmu))
diff --git a/include/linux/perf/arm_pmuv3.h b/include/linux/perf/arm_pmuv3.h
index c2448477c37f..3a5eac11e54d 100644
--- a/include/linux/perf/arm_pmuv3.h
+++ b/include/linux/perf/arm_pmuv3.h
@@ -240,6 +240,14 @@
 #define ARMV8_PMU_OVSR_F		ARMV8_PMU_CNT_MASK_F
 /* Mask for writable bits is both P and C fields */
 #define ARMV8_PMU_OVERFLOWED_MASK	ARMV8_PMU_CNT_MASK_ALL
+
+/* Masks for guest and host counter partitions */
+#define ARMV8_PMU_HPMN_CNT_MASK(N)	GENMASK((N) - 1, 0)
+#define ARMV8_PMU_GUEST_CNT_PART(N)	(ARMV8_PMU_HPMN_CNT_MASK(N) | \
+					 ARMV8_PMU_CNT_MASK_C | \
+					 ARMV8_PMU_CNT_MASK_F)
+#define ARMV8_PMU_HOST_CNT_PART(N)	(ARMV8_PMU_CNT_MASK_ALL & \
+					 ~ARMV8_PMU_GUEST_CNT_PART(N))
 /*
  * PMXEVTYPER: Event selection reg
  */
-- 
2.48.1.601.g30ceb7b040-goog

On 13/02/2025 6:03 pm, Colton Lewis wrote:
> If the PMU is partitioned, keep the driver out of the guest counter
> partition and only use the host counter partition. Partitioning is
> defined by the MDCR_EL2.HPMN register field and saved in
> cpu_pmu->hpmn. The range 0..HPMN-1 is accessible by EL1 and EL0 while
> HPMN..PMCR.N is reserved for EL2.
> 
> Define some macros that take HPMN as an argument and construct
> mutually exclusive bitmaps for testing which partition a particular
> counter is in. Note that despite their different position in the
> bitmap, the cycle and instruction counters are always in the guest
> partition.
> 
> Signed-off-by: Colton Lewis <coltonlewis@google.com>
> ---
>   arch/arm/include/asm/arm_pmuv3.h |  2 +
>   arch/arm64/include/asm/kvm_pmu.h |  5 +++
>   arch/arm64/kvm/pmu-part.c        | 16 +++++++
>   drivers/perf/arm_pmuv3.c         | 73 +++++++++++++++++++++++++++-----
>   include/linux/perf/arm_pmuv3.h   |  8 ++++
>   5 files changed, 94 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm/include/asm/arm_pmuv3.h b/arch/arm/include/asm/arm_pmuv3.h
> index 2ec0e5e83fc9..dadd4ddf51af 100644
> --- a/arch/arm/include/asm/arm_pmuv3.h
> +++ b/arch/arm/include/asm/arm_pmuv3.h
> @@ -227,6 +227,8 @@ static inline bool kvm_set_pmuserenr(u64 val)
>   }
>   
>   static inline void kvm_vcpu_pmu_resync_el0(void) {}
> +static inline void kvm_pmu_host_counters_enable(void) {}
> +static inline void kvm_pmu_host_counters_disable(void) {}
>   
>   /* PMU Version in DFR Register */
>   #define ARMV8_PMU_DFR_VER_NI        0
> diff --git a/arch/arm64/include/asm/kvm_pmu.h b/arch/arm64/include/asm/kvm_pmu.h
> index 174b7f376d95..8f25754fde47 100644
> --- a/arch/arm64/include/asm/kvm_pmu.h
> +++ b/arch/arm64/include/asm/kvm_pmu.h
> @@ -25,6 +25,8 @@ void kvm_host_pmu_init(struct arm_pmu *pmu);
>   u8 kvm_pmu_get_reserved_counters(void);
>   u8 kvm_pmu_hpmn(u8 nr_counters);
>   void kvm_pmu_partition(struct arm_pmu *pmu);
> +void kvm_pmu_host_counters_enable(void);
> +void kvm_pmu_host_counters_disable(void);
>   
>   #else
>   
> @@ -37,6 +39,9 @@ static inline bool kvm_set_pmuserenr(u64 val)
>   static inline void kvm_vcpu_pmu_resync_el0(void) {}
>   static inline void kvm_host_pmu_init(struct arm_pmu *pmu) {}
>   
> +static inline void kvm_pmu_host_counters_enable(void) {}
> +static inline void kvm_pmu_host_counters_disable(void) {}
> +
>   #endif
>   
>   #endif
> diff --git a/arch/arm64/kvm/pmu-part.c b/arch/arm64/kvm/pmu-part.c
> index e74fecc67e37..51da65c678f9 100644
> --- a/arch/arm64/kvm/pmu-part.c
> +++ b/arch/arm64/kvm/pmu-part.c
> @@ -45,3 +45,19 @@ void kvm_pmu_partition(struct arm_pmu *pmu)
>   		pmu->partitioned = false;
>   	}
>   }
> +
> +void kvm_pmu_host_counters_enable(void)
> +{
> +	u64 mdcr = read_sysreg(mdcr_el2);
> +
> +	mdcr |= MDCR_EL2_HPME;
> +	write_sysreg(mdcr, mdcr_el2);
> +}
> +
> +void kvm_pmu_host_counters_disable(void)
> +{
> +	u64 mdcr = read_sysreg(mdcr_el2);
> +
> +	mdcr &= ~MDCR_EL2_HPME;
> +	write_sysreg(mdcr, mdcr_el2);
> +}
> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
> index 0e360feb3432..442dcff56d5b 100644
> --- a/drivers/perf/arm_pmuv3.c
> +++ b/drivers/perf/arm_pmuv3.c
> @@ -730,15 +730,19 @@ static void armv8pmu_disable_event_irq(struct perf_event *event)
>   	armv8pmu_disable_intens(BIT(event->hw.idx));
>   }
>   
> -static u64 armv8pmu_getreset_flags(void)
> +static u64 armv8pmu_getreset_flags(struct arm_pmu *cpu_pmu)
>   {
>   	u64 value;
>   
>   	/* Read */
>   	value = read_pmovsclr();
>   
> +	if (cpu_pmu->partitioned)
> +		value &= ARMV8_PMU_HOST_CNT_PART(cpu_pmu->hpmn);
> +	else
> +		value &= ARMV8_PMU_OVERFLOWED_MASK;
> +
>   	/* Write to clear flags */
> -	value &= ARMV8_PMU_OVERFLOWED_MASK;
>   	write_pmovsclr(value);
>   
>   	return value;
> @@ -765,6 +769,18 @@ static void armv8pmu_disable_user_access(void)
>   	update_pmuserenr(0);
>   }
>   
> +static bool armv8pmu_is_guest_part(struct arm_pmu *cpu_pmu, u8 idx)
> +{
> +	return cpu_pmu->partitioned &&
> +		(BIT(idx) & ARMV8_PMU_GUEST_CNT_PART(cpu_pmu->hpmn));
> +}
> +
> +static bool armv8pmu_is_host_part(struct arm_pmu *cpu_pmu, u8 idx)
> +{
> +	return !cpu_pmu->partitioned ||
> +		(BIT(idx) & ARMV8_PMU_HOST_CNT_PART(cpu_pmu->hpmn));
> +}
> +
>   static void armv8pmu_enable_user_access(struct arm_pmu *cpu_pmu)
>   {
>   	int i;
> @@ -773,6 +789,8 @@ static void armv8pmu_enable_user_access(struct arm_pmu *cpu_pmu)
>   	if (is_pmuv3p9(cpu_pmu->pmuver)) {
>   		u64 mask = 0;
>   		for_each_set_bit(i, cpuc->used_mask, ARMPMU_MAX_HWEVENTS) {
> +			if (armv8pmu_is_guest_part(cpu_pmu, i))
> +				continue;

Hi Colton,

Is it possible to keep the guest bits out of used_mask and cntr_mask in 
the first place? Then all these loops don't need to have the logic for 
is_guest_part()/is_host_part().

That leads me to wonder about updating the printout:

  hw perfevents: enabled with armv8_pmuv3_0 PMU driver, 7 (0,8000003f)
    counters available

It might be a bit confusing if that doesn't quite reflect reality anymore.

Thanks
James

James Clark <james.clark@linaro.org> writes:

> On 13/02/2025 6:03 pm, Colton Lewis wrote:
>> If the PMU is partitioned, keep the driver out of the guest counter
>> partition and only use the host counter partition. Partitioning is
>> defined by the MDCR_EL2.HPMN register field and saved in
>> cpu_pmu->hpmn. The range 0..HPMN-1 is accessible by EL1 and EL0 while
>> HPMN..PMCR.N is reserved for EL2.

>> Define some macros that take HPMN as an argument and construct
>> mutually exclusive bitmaps for testing which partition a particular
>> counter is in. Note that despite their different position in the
>> bitmap, the cycle and instruction counters are always in the guest
>> partition.

>> Signed-off-by: Colton Lewis <coltonlewis@google.com>
>> ---
>>    arch/arm/include/asm/arm_pmuv3.h |  2 +
>>    arch/arm64/include/asm/kvm_pmu.h |  5 +++
>>    arch/arm64/kvm/pmu-part.c        | 16 +++++++
>>    drivers/perf/arm_pmuv3.c         | 73 +++++++++++++++++++++++++++-----
>>    include/linux/perf/arm_pmuv3.h   |  8 ++++
>>    5 files changed, 94 insertions(+), 10 deletions(-)

>> diff --git a/arch/arm/include/asm/arm_pmuv3.h  
>> b/arch/arm/include/asm/arm_pmuv3.h
>> index 2ec0e5e83fc9..dadd4ddf51af 100644
>> --- a/arch/arm/include/asm/arm_pmuv3.h
>> +++ b/arch/arm/include/asm/arm_pmuv3.h
>> @@ -227,6 +227,8 @@ static inline bool kvm_set_pmuserenr(u64 val)
>>    }

>>    static inline void kvm_vcpu_pmu_resync_el0(void) {}
>> +static inline void kvm_pmu_host_counters_enable(void) {}
>> +static inline void kvm_pmu_host_counters_disable(void) {}

>>    /* PMU Version in DFR Register */
>>    #define ARMV8_PMU_DFR_VER_NI        0
>> diff --git a/arch/arm64/include/asm/kvm_pmu.h  
>> b/arch/arm64/include/asm/kvm_pmu.h
>> index 174b7f376d95..8f25754fde47 100644
>> --- a/arch/arm64/include/asm/kvm_pmu.h
>> +++ b/arch/arm64/include/asm/kvm_pmu.h
>> @@ -25,6 +25,8 @@ void kvm_host_pmu_init(struct arm_pmu *pmu);
>>    u8 kvm_pmu_get_reserved_counters(void);
>>    u8 kvm_pmu_hpmn(u8 nr_counters);
>>    void kvm_pmu_partition(struct arm_pmu *pmu);
>> +void kvm_pmu_host_counters_enable(void);
>> +void kvm_pmu_host_counters_disable(void);

>>    #else

>> @@ -37,6 +39,9 @@ static inline bool kvm_set_pmuserenr(u64 val)
>>    static inline void kvm_vcpu_pmu_resync_el0(void) {}
>>    static inline void kvm_host_pmu_init(struct arm_pmu *pmu) {}

>> +static inline void kvm_pmu_host_counters_enable(void) {}
>> +static inline void kvm_pmu_host_counters_disable(void) {}
>> +
>>    #endif

>>    #endif
>> diff --git a/arch/arm64/kvm/pmu-part.c b/arch/arm64/kvm/pmu-part.c
>> index e74fecc67e37..51da65c678f9 100644
>> --- a/arch/arm64/kvm/pmu-part.c
>> +++ b/arch/arm64/kvm/pmu-part.c
>> @@ -45,3 +45,19 @@ void kvm_pmu_partition(struct arm_pmu *pmu)
>>    		pmu->partitioned = false;
>>    	}
>>    }
>> +
>> +void kvm_pmu_host_counters_enable(void)
>> +{
>> +	u64 mdcr = read_sysreg(mdcr_el2);
>> +
>> +	mdcr |= MDCR_EL2_HPME;
>> +	write_sysreg(mdcr, mdcr_el2);
>> +}
>> +
>> +void kvm_pmu_host_counters_disable(void)
>> +{
>> +	u64 mdcr = read_sysreg(mdcr_el2);
>> +
>> +	mdcr &= ~MDCR_EL2_HPME;
>> +	write_sysreg(mdcr, mdcr_el2);
>> +}
>> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
>> index 0e360feb3432..442dcff56d5b 100644
>> --- a/drivers/perf/arm_pmuv3.c
>> +++ b/drivers/perf/arm_pmuv3.c
>> @@ -730,15 +730,19 @@ static void armv8pmu_disable_event_irq(struct  
>> perf_event *event)
>>    	armv8pmu_disable_intens(BIT(event->hw.idx));
>>    }

>> -static u64 armv8pmu_getreset_flags(void)
>> +static u64 armv8pmu_getreset_flags(struct arm_pmu *cpu_pmu)
>>    {
>>    	u64 value;

>>    	/* Read */
>>    	value = read_pmovsclr();

>> +	if (cpu_pmu->partitioned)
>> +		value &= ARMV8_PMU_HOST_CNT_PART(cpu_pmu->hpmn);
>> +	else
>> +		value &= ARMV8_PMU_OVERFLOWED_MASK;
>> +
>>    	/* Write to clear flags */
>> -	value &= ARMV8_PMU_OVERFLOWED_MASK;
>>    	write_pmovsclr(value);

>>    	return value;
>> @@ -765,6 +769,18 @@ static void armv8pmu_disable_user_access(void)
>>    	update_pmuserenr(0);
>>    }

>> +static bool armv8pmu_is_guest_part(struct arm_pmu *cpu_pmu, u8 idx)
>> +{
>> +	return cpu_pmu->partitioned &&
>> +		(BIT(idx) & ARMV8_PMU_GUEST_CNT_PART(cpu_pmu->hpmn));
>> +}
>> +
>> +static bool armv8pmu_is_host_part(struct arm_pmu *cpu_pmu, u8 idx)
>> +{
>> +	return !cpu_pmu->partitioned ||
>> +		(BIT(idx) & ARMV8_PMU_HOST_CNT_PART(cpu_pmu->hpmn));
>> +}
>> +
>>    static void armv8pmu_enable_user_access(struct arm_pmu *cpu_pmu)
>>    {
>>    	int i;
>> @@ -773,6 +789,8 @@ static void armv8pmu_enable_user_access(struct  
>> arm_pmu *cpu_pmu)
>>    	if (is_pmuv3p9(cpu_pmu->pmuver)) {
>>    		u64 mask = 0;
>>    		for_each_set_bit(i, cpuc->used_mask, ARMPMU_MAX_HWEVENTS) {
>> +			if (armv8pmu_is_guest_part(cpu_pmu, i))
>> +				continue;

> Hi Colton,

> Is it possible to keep the guest bits out of used_mask and cntr_mask in
> the first place? Then all these loops don't need to have the logic for
> is_guest_part()/is_host_part().

It should be possible.

> That leads me to wonder about updating the printout:

>    hw perfevents: enabled with armv8_pmuv3_0 PMU driver, 7 (0,8000003f)
>      counters available

> It might be a bit confusing if that doesn't quite reflect reality anymore.

Good point.