KVM: arm64: PMU: Fix GET_ONE_REG for vPMC regs to return the current value

Have KVM_GET_ONE_REG for vPMU counter (vPMC) registers (PMCCNTR_EL0
and PMEVCNTR<n>_EL0) return the sum of the register value in the sysreg
file and the current perf event counter value.

Values of vPMC registers are saved in sysreg files on certain occasions.
These saved values don't represent the current values of the vPMC
registers if the perf events for the vPMCs count events after the save.
The current values of those registers are the sum of the sysreg file
value and the current perf event counter value.  But, when userspace
reads those registers (using KVM_GET_ONE_REG), KVM returns the sysreg
file value to userspace (not the sum value).

Fix this to return the sum value for KVM_GET_ONE_REG.

Fixes: 051ff581 ("arm64: KVM: Add access handler for event counter register")
Cc: stable@vger.kernel.org
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Reiji Watanabe <reijiw@google.com>
Link: https://lore.kernel.org/r/20230313033208.1475499-1-reijiw@google.comSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kvm/sys_regs.c

@@ -856,6 +856,22 @@ static bool pmu_counter_idx_valid(struct kvm_vcpu *vcpu, u64 idx)
 	return true;
 }
 
+static int get_pmu_evcntr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
+			  u64 *val)
+{
+	u64 idx;
+
+	if (r->CRn == 9 && r->CRm == 13 && r->Op2 == 0)
+		/* PMCCNTR_EL0 */
+		idx = ARMV8_PMU_CYCLE_IDX;
+	else
+		/* PMEVCNTRn_EL0 */
+		idx = ((r->CRm & 3) << 3) | (r->Op2 & 7);
+
+	*val = kvm_pmu_get_counter_value(vcpu, idx);
+	return 0;
+}
+
 static bool access_pmu_evcntr(struct kvm_vcpu *vcpu,
 			      struct sys_reg_params *p,
 			      const struct sys_reg_desc *r)
@@ -1072,7 +1088,7 @@ static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 /* Macro to expand the PMEVCNTRn_EL0 register */
 #define PMU_PMEVCNTR_EL0(n)						\
 	{ PMU_SYS_REG(SYS_PMEVCNTRn_EL0(n)),				\
-	  .reset = reset_pmevcntr,					\
+	  .reset = reset_pmevcntr, .get_user = get_pmu_evcntr,		\
 	  .access = access_pmu_evcntr, .reg = (PMEVCNTR0_EL0 + n), }
 
 /* Macro to expand the PMEVTYPERn_EL0 register */
@@ -1982,7 +1998,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ PMU_SYS_REG(SYS_PMCEID1_EL0),
 	  .access = access_pmceid, .reset = NULL },
 	{ PMU_SYS_REG(SYS_PMCCNTR_EL0),
-	  .access = access_pmu_evcntr, .reset = reset_unknown, .reg = PMCCNTR_EL0 },
+	  .access = access_pmu_evcntr, .reset = reset_unknown,
+	  .reg = PMCCNTR_EL0, .get_user = get_pmu_evcntr},
 	{ PMU_SYS_REG(SYS_PMXEVTYPER_EL0),
 	  .access = access_pmu_evtyper, .reset = NULL },
 	{ PMU_SYS_REG(SYS_PMXEVCNTR_EL0),