Currently if a guest is live-migrated while it is actively using perf counters, then after live-migrate it will notice that all counters would suddenly start reporting 0s. This is due to the fact we are not re-creating the relevant perf events inside the kernel. Usually on live-migration guest state is restored using KVM_SET_ONE_REG ioctl interface, which simply restores the value of PMU registers values but does not re-program the perf events so that the guest can seamlessly use these counters even after live-migration like it was doing before live-migration. Instead there are two completely different code path between guest accessing PMU registers and VMM restoring counters on live-migration. In case of KVM_SET_ONE_REG: kvm_arm_set_reg() ...... kvm_arm_sys_reg_set_reg() ........... reg_from_user() but in case when guest tries to access these counters: handle_exit() ..... kvm_handle_sys_reg() ..........perform_access() ...............access_pmu_evcntr() ...................kvm_pmu_set_counter_value() .......................kvm_pmu_create_perf_event() The drawback of using the KVM_SET_ONE_REG interface is that the host pmu events which were registered for the source instance are not present for the destination instance. Thus, passively restoring PMCR_EL0 using KVM_SET_ONE_REG interface would not create the necessary host pmu events which are crucial for seamless guest experience across live migration. In ordet to fix the situation, on first vcpu load we should restore PMCR_EL0 in the same exact way like the guest was trying to access these counters. And then we will also recreate the relevant host pmu events. Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> Signed-off-by: Jinank Jain <jinankj@xxxxxxxxx> Cc: Alexander Graf (AWS) <graf@xxxxxxxxx> Cc: Marc Zyngier <maz@xxxxxxxxxx> Cc: James Morse <james.morse@xxxxxxx> Cc: Alexandru Elisei <alexandru.elisei@xxxxxxx> Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> --- arch/arm64/include/asm/kvm_host.h | 1 + arch/arm64/kvm/arm.c | 4 ++++ arch/arm64/kvm/pmu-emul.c | 3 +++ 3 files changed, 8 insertions(+) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index 7cd7d5c8c4bc..6336b4309114 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -46,6 +46,7 @@ #define KVM_REQ_VCPU_RESET KVM_ARCH_REQ(2) #define KVM_REQ_RECORD_STEAL KVM_ARCH_REQ(3) #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4) +#define KVM_REQ_RELOAD_PMU KVM_ARCH_REQ(5) #define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \ KVM_DIRTY_LOG_INITIALLY_SET) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index e720148232a0..facf4d41d32a 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -689,6 +689,10 @@ static void check_vcpu_requests(struct kvm_vcpu *vcpu) vgic_v4_load(vcpu); preempt_enable(); } + + if (kvm_check_request(KVM_REQ_RELOAD_PMU, vcpu)) + kvm_pmu_handle_pmcr(vcpu, + __vcpu_sys_reg(vcpu, PMCR_EL0)); } } diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c index fd167d4f4215..a0bbb7111f57 100644 --- a/arch/arm64/kvm/pmu-emul.c +++ b/arch/arm64/kvm/pmu-emul.c @@ -850,6 +850,9 @@ int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu) return -EINVAL; } + /* One-off reload of the PMU on first run */ + kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu); + return 0; } -- 2.31.1 Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879 _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
