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authorAlexandru Elisei <alexandru.elisei@arm.com>2022-01-27 17:17:58 +0100
committerMarc Zyngier <maz@kernel.org>2022-02-08 18:51:21 +0100
commit6ee7fca2a4a023b14aa1f1f3c4f6c833116116ef (patch)
treeebdd88fbcc0e271e78a68e2bba91bc1b29367a41 /tools/arch/arm64
parentKVM: arm64: Keep a list of probed PMUs (diff)
downloadlinux-6ee7fca2a4a023b14aa1f1f3c4f6c833116116ef.tar.xz
linux-6ee7fca2a4a023b14aa1f1f3c4f6c833116116ef.zip
KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute
When KVM creates an event and there are more than one PMUs present on the system, perf_init_event() will go through the list of available PMUs and will choose the first one that can create the event. The order of the PMUs in this list depends on the probe order, which can change under various circumstances, for example if the order of the PMU nodes change in the DTB or if asynchronous driver probing is enabled on the kernel command line (with the driver_async_probe=armv8-pmu option). Another consequence of this approach is that on heteregeneous systems all virtual machines that KVM creates will use the same PMU. This might cause unexpected behaviour for userspace: when a VCPU is executing on the physical CPU that uses this default PMU, PMU events in the guest work correctly; but when the same VCPU executes on another CPU, PMU events in the guest will suddenly stop counting. Fortunately, perf core allows user to specify on which PMU to create an event by using the perf_event_attr->type field, which is used by perf_init_event() as an index in the radix tree of available PMUs. Add the KVM_ARM_VCPU_PMU_V3_CTRL(KVM_ARM_VCPU_PMU_V3_SET_PMU) VCPU attribute to allow userspace to specify the arm_pmu that KVM will use when creating events for that VCPU. KVM will make no attempt to run the VCPU on the physical CPUs that share the PMU, leaving it up to userspace to manage the VCPU threads' affinity accordingly. To ensure that KVM doesn't expose an asymmetric system to the guest, the PMU set for one VCPU will be used by all other VCPUs. Once a VCPU has run, the PMU cannot be changed in order to avoid changing the list of available events for a VCPU, or to change the semantics of existing events. Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20220127161759.53553-6-alexandru.elisei@arm.com
Diffstat (limited to 'tools/arch/arm64')
-rw-r--r--tools/arch/arm64/include/uapi/asm/kvm.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/tools/arch/arm64/include/uapi/asm/kvm.h b/tools/arch/arm64/include/uapi/asm/kvm.h
index b3edde68bc3e..1d0a0a2a9711 100644
--- a/tools/arch/arm64/include/uapi/asm/kvm.h
+++ b/tools/arch/arm64/include/uapi/asm/kvm.h
@@ -362,6 +362,7 @@ struct kvm_arm_copy_mte_tags {
#define KVM_ARM_VCPU_PMU_V3_IRQ 0
#define KVM_ARM_VCPU_PMU_V3_INIT 1
#define KVM_ARM_VCPU_PMU_V3_FILTER 2
+#define KVM_ARM_VCPU_PMU_V3_SET_PMU 3
#define KVM_ARM_VCPU_TIMER_CTRL 1
#define KVM_ARM_VCPU_TIMER_IRQ_VTIMER 0
#define KVM_ARM_VCPU_TIMER_IRQ_PTIMER 1