The astute user can still look into the TRM for their CPU and find out
they've been cheated, though. Nobody's perfect.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/pmu-emul.c | 29 +++++++++++++++++++++++++++++
 arch/arm64/kvm/sys_regs.c |  5 +----
 include/kvm/arm_pmu.h     |  5 +++++
 3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 67a731bafbc9..0458860bade2 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c

@@ -765,6 +765,35 @@ static int kvm_pmu_probe_pmuver(void)
 	return pmuver;
 }
 
+u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
+{
+	unsigned long *bmap = vcpu->kvm->arch.pmu_filter;
+	u64 val, mask = 0;
+	int base, i;
+
+	if (!pmceid1) {
+		val = read_sysreg(pmceid0_el0);
+		base = 0;
+	} else {
+		val = read_sysreg(pmceid1_el0);
+		base = 32;
+	}
+
+	if (!bmap)
+		return val;
+
+	for (i = 0; i < 32; i += 8) {

+		u64 byte;
+
+		byte = bitmap_get_value8(bmap, base + i);
+		mask |= byte << i;
+		byte = bitmap_get_value8(bmap, 0x4000 + base + i);
+		mask |= byte << (32 + i);
+	}
+
+	return val & mask;
+}
+
 bool kvm_arm_support_pmu_v3(void)
 {
 	/*

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 077293b5115f..20ab2a7d37ca 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c

@@ -769,10 +769,7 @@ static bool access_pmceid(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 	if (pmu_access_el0_disabled(vcpu))
 		return false;
 
-	if (!(p->Op2 & 1))
-		pmceid = read_sysreg(pmceid0_el0);
-	else
-		pmceid = read_sysreg(pmceid1_el0);
+	pmceid = kvm_pmu_get_pmceid(vcpu, (p->Op2 & 1));
 
 	p->regval = pmceid;
 

diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
index 6db030439e29..98cbfe885a53 100644
--- a/include/kvm/arm_pmu.h
+++ b/include/kvm/arm_pmu.h

@@ -34,6 +34,7 @@ struct kvm_pmu {
 u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx);
 void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val);
 u64 kvm_pmu_valid_counter_mask(struct kvm_vcpu *vcpu);
+u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1);
 void kvm_pmu_vcpu_init(struct kvm_vcpu *vcpu);
 void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu);
 void kvm_pmu_vcpu_destroy(struct kvm_vcpu *vcpu);

@@ -108,6 +109,10 @@ static inline int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu)
 {
 	return 0;
 }
+static inline u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
+{
+	return 0;
+}
 #endif
 
 #endif