Re: [PATCH v4 4/6] kvm powerpc/book3s-apiv2: Introduce kvm-hv specific PMU

> On 24 Feb 2025, at 6:45=E2=80=AFPM, Vaibhav Jain =
<[email protected]> wrote:
>=20
> Introduce a new PMU named 'kvm-hv' inside a new module named =
'kvm-hv-pmu'
> to report Book3s kvm-hv specific performance counters. This will =
expose
> KVM-HV specific performance attributes to user-space via kernel's PMU
> infrastructure and would enableusers to monitor active kvm-hv based =
guests.
>=20
> The patch creates necessary scaffolding to for the new PMU callbacks =
and
> introduces the new kernel module name 'kvm-hv-pmu' which is built with
> CONFIG_KVM_BOOK3S_HV_PMU. The patch doesn't introduce any perf-events =
yet,
> which will be introduced in later patches
>=20
> Signed-off-by: Vaibhav Jain <[email protected]>
>=20
> ---
> Changelog
>=20
> v3->v4:
> * Introduced a new kernel module named 'kmv-hv-pmu' to host the new =
PMU
> instead of building the as part of KVM-HV module. [ Maddy ]
> * Moved the code from arch/powerpc/kvm to arch/powerpc/perf [ Atheera =
]
> * Added a new config named KVM_BOOK3S_HV_PMU to =
arch/powerpc/kvm/Kconfig
>=20
> v2->v3:
> * Fixed a build warning reported by kernel build robot.
> Link:
> =
https://lore.kernel.org/oe-kbuild-all/[email protected]
>=20
> v1->v2:
> * Fixed an issue of kvm-hv not loading on baremetal kvm [Gautam]
> ---
> arch/powerpc/kvm/Kconfig       |  13 ++++
> arch/powerpc/perf/Makefile     |   2 +
> arch/powerpc/perf/kvm-hv-pmu.c | 138 +++++++++++++++++++++++++++++++++
> 3 files changed, 153 insertions(+)
> create mode 100644 arch/powerpc/perf/kvm-hv-pmu.c
>=20
> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
> index dbfdc126bf14..5f0ce19e7e27 100644
> --- a/arch/powerpc/kvm/Kconfig
> +++ b/arch/powerpc/kvm/Kconfig
> @@ -83,6 +83,7 @@ config KVM_BOOK3S_64_HV
> depends on KVM_BOOK3S_64 && PPC_POWERNV
> select KVM_BOOK3S_HV_POSSIBLE
> select KVM_GENERIC_MMU_NOTIFIER
> + select KVM_BOOK3S_HV_PMU
> select CMA
> help
>  Support running unmodified book3s_64 guest kernels in
> @@ -171,6 +172,18 @@ config KVM_BOOK3S_HV_NESTED_PMU_WORKAROUND
>  those buggy L1s which saves the L2 state, at the cost of performance
>  in all nested-capable guest entry/exit.
>=20
> +config KVM_BOOK3S_HV_PMU
> + tristate "Hypervisor Perf events for KVM Book3s-HV"
> + depends on KVM_BOOK3S_64_HV && HV_PERF_CTRS
> + help
> +  Enable Book3s-HV Hypervisor Perf events PMU named 'kvm-hv'. These
> +  Perf events give an overview of hypervisor performance overall
> +  instead of a specific guests. Currently the PMU reports
> +  L0-Hypervisor stats on a kvm-hv enabled PSeries LPAR like:
> +  * Total/Used Guest-Heap
> +  * Total/Used Guest Page-table Memory
> +  * Total amount of Guest Page-table Memory reclaimed
> +
> config KVM_BOOKE_HV
> bool
>=20
> diff --git a/arch/powerpc/perf/Makefile b/arch/powerpc/perf/Makefile
> index ac2cf58d62db..7f53fcb7495a 100644
> --- a/arch/powerpc/perf/Makefile
> +++ b/arch/powerpc/perf/Makefile
> @@ -18,6 +18,8 @@ obj-$(CONFIG_HV_PERF_CTRS) +=3D hv-24x7.o hv-gpci.o =
hv-common.o
>=20
> obj-$(CONFIG_VPA_PMU) +=3D vpa-pmu.o
>=20
> +obj-$(CONFIG_KVM_BOOK3S_HV_PMU) +=3D kvm-hv-pmu.o
> +
> obj-$(CONFIG_PPC_8xx) +=3D 8xx-pmu.o
>=20
> obj-$(CONFIG_PPC64) +=3D $(obj64-y)
> diff --git a/arch/powerpc/perf/kvm-hv-pmu.c =
b/arch/powerpc/perf/kvm-hv-pmu.c
> new file mode 100644
> index 000000000000..c154f54e09e2
> --- /dev/null
> +++ b/arch/powerpc/perf/kvm-hv-pmu.c
> @@ -0,0 +1,138 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Description: PMUs specific to running nested KVM-HV guests
> + * on Book3S processors (specifically POWER9 and later).
> + */
> +
> +#define pr_fmt(fmt)  "kvmppc-pmu: " fmt
> +
> +#include "asm-generic/local64.h"
> +#include <linux/kernel.h>
> +#include <linux/errno.h>
> +#include <linux/ratelimit.h>
> +#include <linux/kvm_host.h>
> +#include <linux/gfp_types.h>
> +#include <linux/pgtable.h>
> +#include <linux/perf_event.h>
> +#include <linux/spinlock_types.h>
> +#include <linux/spinlock.h>
> +
> +#include <asm/types.h>
> +#include <asm/kvm_ppc.h>
> +#include <asm/kvm_book3s.h>
> +#include <asm/mmu.h>
> +#include <asm/pgalloc.h>
> +#include <asm/pte-walk.h>
> +#include <asm/reg.h>
> +#include <asm/plpar_wrappers.h>
> +#include <asm/firmware.h>
> +
> +enum kvmppc_pmu_eventid {
> + KVMPPC_EVENT_MAX,
> +};
> +
> +static struct attribute *kvmppc_pmu_events_attr[] =3D {
> + NULL,
> +};
> +
> +static const struct attribute_group kvmppc_pmu_events_group =3D {
> + .name =3D "events",
> + .attrs =3D kvmppc_pmu_events_attr,
> +};
> +
> +PMU_FORMAT_ATTR(event, "config:0");
> +static struct attribute *kvmppc_pmu_format_attr[] =3D {
> + &format_attr_event.attr,
> + NULL,
> +};
> +
> +static struct attribute_group kvmppc_pmu_format_group =3D {
> + .name =3D "format",
> + .attrs =3D kvmppc_pmu_format_attr,
> +};
> +
> +static const struct attribute_group *kvmppc_pmu_attr_groups[] =3D {
> + &kvmppc_pmu_events_group,
> + &kvmppc_pmu_format_group,
> + NULL,
> +};
> +
> +static int kvmppc_pmu_event_init(struct perf_event *event)
> +{
> + unsigned int config =3D event->attr.config;
> +
> + pr_debug("%s: Event(%p) id=3D%llu cpu=3D%x on_cpu=3D%x config=3D%u",
> + __func__, event, event->id, event->cpu,
> + event->oncpu, config);
> +
> + if (event->attr.type !=3D event->pmu->type)
> + return -ENOENT;
> +
> + if (config >=3D KVMPPC_EVENT_MAX)
> + return -EINVAL;
> +
> + local64_set(&event->hw.prev_count, 0);
> + local64_set(&event->count, 0);
> +
> + return 0;
> +}
> +
> +static void kvmppc_pmu_del(struct perf_event *event, int flags)
> +{
> +}
> +
> +static int kvmppc_pmu_add(struct perf_event *event, int flags)
> +{
> + return 0;
> +}
> +
> +static void kvmppc_pmu_read(struct perf_event *event)
> +{
> +}
> +
> +/* L1 wide counters PMU */
> +static struct pmu kvmppc_pmu =3D {
> + .module =3D THIS_MODULE,
> + .task_ctx_nr =3D perf_sw_context,
> + .name =3D "kvm-hv",
> + .event_init =3D kvmppc_pmu_event_init,
> + .add =3D kvmppc_pmu_add,
> + .del =3D kvmppc_pmu_del,
> + .read =3D kvmppc_pmu_read,
> + .attr_groups =3D kvmppc_pmu_attr_groups,
> + .type =3D -1,
> +};
> +
> +static int __init kvmppc_register_pmu(void)
> +{
> + int rc =3D -EOPNOTSUPP;
> +
> + /* only support events for nestedv2 right now */
> + if (kvmhv_is_nestedv2()) {

We don=E2=80=99t need PVR check here ? Description of module says this =
is supported for power9 and later.
> + /* Setup done now register the PMU */
> + pr_info("Registering kvm-hv pmu");
> +
> + /* Register only if we arent already registered */
Not sure why we need this=E2=80=A6 Have you seen any issue without this =
? I don=E2=80=99t see any similar check in arch/powerpc/perf/vpa-pmu.c ,

> + rc =3D (kvmppc_pmu.type =3D=3D -1) ?
> +     perf_pmu_register(&kvmppc_pmu, kvmppc_pmu.name,
> +       -1) : 0;
> + }
> +
> + return rc;
> +}
> +
> +static void __exit kvmppc_unregister_pmu(void)
> +{
> + if (kvmhv_is_nestedv2()) {
> + if (kvmppc_pmu.type !=3D -1)
> + perf_pmu_unregister(&kvmppc_pmu);
> +
> + pr_info("kvmhv_pmu unregistered.\n");
> + }
> +}
> +
> +module_init(kvmppc_register_pmu);
> +module_exit(kvmppc_unregister_pmu);
> +MODULE_DESCRIPTION("KVM PPC Book3s-hv PMU");
> +MODULE_AUTHOR("Vaibhav Jain <[email protected]>");
> +MODULE_LICENSE("GPL");
> --=20
> 2.48.1
>=20
>=20
>=20