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Re: [PATCH v4] arm/kvm: Enable support for KVM_ARM_VCPU_PMU_V3_FILTER


From: Eric Auger
Subject: Re: [PATCH v4] arm/kvm: Enable support for KVM_ARM_VCPU_PMU_V3_FILTER
Date: Thu, 14 Dec 2023 19:13:15 +0100
User-agent: Mozilla Thunderbird

Hi Shaoqin,

On 12/7/23 11:36, Shaoqin Huang wrote:
> The KVM_ARM_VCPU_PMU_V3_FILTER provide the ability to let the VMM decide
> which PMU events are provided to the guest. Add a new option
> `pmu-filter` as -accel sub-option to set the PMU Event Filtering.
> Without the filter, the KVM will expose all events from the host to
> guest by default.
> 
> The `pmu-filter` has such format:
> 
>   pmu-filter="{A,D}:start-end[;{A,D}:start-end...]"
> 
> The A means "allow" and D means "deny", start is the first event of the
> range and the end is the last one. The first registered range defines
> the global policy(global ALLOW if the first @action is DENY, global DENY
> if the first @action is ALLOW). The start and end only support hex
> format now. For example:
> 
>   pmu-filter="A:0x11-0x11;A:0x23-0x3a;D:0x30-0x30"
> 
> Since the first action is allow, we have a global deny policy. It
> will allow event 0x11 (The cycle counter), events 0x23 to 0x3a is
> also allowed except the event 0x30 is denied, and all the other events
> are disallowed.
> 
> Here is an real example shows how to use the PMU Event Filtering, when
> we launch a guest by use kvm, add such command line:
> 
>   # qemu-system-aarch64 \
>       -accel kvm,pmu-filter="D:0x11-0x11"
> 
> Since the first action is deny, we have a global allow policy. This
> disables the filtering of the cycle counter (event 0x11 being CPU_CYCLES).
> 
> And then in guest, use the perf to count the cycle:
> 
>   # perf stat sleep 1
> 
>    Performance counter stats for 'sleep 1':
> 
>               1.22 msec task-clock                       #    0.001 CPUs 
> utilized
>                  1      context-switches                 #  820.695 /sec
>                  0      cpu-migrations                   #    0.000 /sec
>                 55      page-faults                      #   45.138 K/sec
>    <not supported>      cycles
>            1128954      instructions
>             227031      branches                         #  186.323 M/sec
>               8686      branch-misses                    #    3.83% of all 
> branches
> 
>        1.002492480 seconds time elapsed
> 
>        0.001752000 seconds user
>        0.000000000 seconds sys
> 
> As we can see, the cycle counter has been disabled in the guest, but
> other pmu events are still work.
> 
> Signed-off-by: Shaoqin Huang <shahuang@redhat.com>
> ---
> v3->v4:
>   - Fix the wrong check for pmu_filter_init.            [Sebastian]
>   - Fix multiple alignment issue.                       [Gavin]
>   - Report error by warn_report() instead of error_report(), and don't use
>   abort() since the PMU Event Filter is an add-on and best-effort feature.
>                                                         [Gavin]
>   - Add several missing {  } for single line of code.   [Gavin]
>   - Use the g_strsplit() to replace strtok().           [Gavin]
> 
> v2->v3:
>   - Improve commits message, use kernel doc wording, add more explaination on
>     filter example, fix some typo error.                [Eric]
>   - Add g_free() in kvm_arch_set_pmu_filter() to prevent memory leak. [Eric]
>   - Add more precise error message report.              [Eric]
>   - In options doc, add pmu-filter rely on KVM_ARM_VCPU_PMU_V3_FILTER support 
> in
>     KVM.                                                [Eric]
> 
> v1->v2:
>   - Add more description for allow and deny meaning in 
>     commit message.                                     [Sebastian]
>   - Small improvement.                                  [Sebastian]
> 
> v2: https://lore.kernel.org/all/20231117060838.39723-1-shahuang@redhat.com/
> v1: https://lore.kernel.org/all/20231113081713.153615-1-shahuang@redhat.com/
> ---
>  include/sysemu/kvm_int.h |  1 +
>  qemu-options.hx          | 21 +++++++++++
>  target/arm/kvm.c         | 23 ++++++++++++
>  target/arm/kvm64.c       | 75 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 120 insertions(+)
> 
> diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
> index fd846394be..8f4601474f 100644
> --- a/include/sysemu/kvm_int.h
> +++ b/include/sysemu/kvm_int.h
> @@ -120,6 +120,7 @@ struct KVMState
>      uint32_t xen_caps;
>      uint16_t xen_gnttab_max_frames;
>      uint16_t xen_evtchn_max_pirq;
> +    char *kvm_pmu_filter;
>  };
>  
>  void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml,
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 42fd09e4de..054865ba0d 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -187,6 +187,7 @@ DEF("accel", HAS_ARG, QEMU_OPTION_accel,
>      "                tb-size=n (TCG translation block cache size)\n"
>      "                dirty-ring-size=n (KVM dirty ring GFN count, default 
> 0)\n"
>      "                eager-split-size=n (KVM Eager Page Split chunk size, 
> default 0, disabled. ARM only)\n"
> +    "                pmu-filter={A,D}:start-end[;{A,D}:start-end...] (KVM 
> PMU Event Filter, default no filter. ARM only)\n"
Sorry for coming back late with this kind of comment but I am not
comfortable with the pmu-filter being an accel suboption. Why isn't it a
cpu option instead like the pmu option?

qemu-system-aarch64 -M virt -cpu
max,pmu-filter="A:0x11-0x11;A:0x23-0x3a;D:0x30-0x30",sve=on,sve128=on,sve256=on

See https://qemu-project.gitlab.io/qemu/system/arm/cpu-features.html

Wouldn't it make more sense? The PMU filter control is a vcpu device
ctrl, isn't it.


>      "                
> notify-vmexit=run|internal-error|disable,notify-window=n (enable notify VM 
> exit and set notify window, x86 only)\n"
>      "                thread=single|multi (enable multi-threaded TCG)\n", 
> QEMU_ARCH_ALL)
>  SRST
> @@ -259,6 +260,26 @@ SRST
>          impact on the memory. By default, this feature is disabled
>          (eager-split-size=0).
>  
> +    ``pmu-filter={A,D}:start-end[;{A,D}:start-end...]``
> +        KVM implements PMU Event Filtering to prevent a guest from being 
> able to
> +        sample certain events. It depends on the KVM_ARM_VCPU_PMU_V3_FILTER
> +        attribute supported in KVM. It has the following format:
> +
> +        pmu-filter="{A,D}:start-end[;{A,D}:start-end...]"
> +
> +        The A means "allow" and D means "deny", start is the first event of 
> the
> +        range and the end is the last one. The first registered range defines
> +        the global policy(global ALLOW if the first @action is DENY, global 
> DENY
> +        if the first @action is ALLOW). The start and end only support hex
> +        format now. For example:
> +
> +        pmu-filter="A:0x11-0x11;A:0x23-0x3a;D:0x30-0x30"
> +
> +        Since the first action is allow, we have a global deny policy. It
> +        will allow event 0x11 (The cycle counter), events 0x23 to 0x3a is
> +        also allowed except the event 0x30 is denied, and all the other 
> events
> +        are disallowed.
> +
>      ``notify-vmexit=run|internal-error|disable,notify-window=n``
>          Enables or disables notify VM exit support on x86 host and specify
>          the corresponding notify window to trigger the VM exit if enabled.
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 7903e2ddde..1f73b83674 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -1108,6 +1108,22 @@ static void kvm_arch_set_eager_split_size(Object *obj, 
> Visitor *v,
>      s->kvm_eager_split_size = value;
>  }
>  
> +static char *kvm_arch_get_pmu_filter(Object *obj, Error **errp)
> +{
> +    KVMState *s = KVM_STATE(obj);
> +
> +    return g_strdup(s->kvm_pmu_filter);
> +}
> +
> +static void kvm_arch_set_pmu_filter(Object *obj, const char *pmu_filter,
> +                                    Error **errp)
> +{
> +    KVMState *s = KVM_STATE(obj);
> +
> +    g_free(s->kvm_pmu_filter);
> +    s->kvm_pmu_filter = g_strdup(pmu_filter);
> +}
> +
>  void kvm_arch_accel_class_init(ObjectClass *oc)
>  {
>      object_class_property_add(oc, "eager-split-size", "size",
> @@ -1116,4 +1132,11 @@ void kvm_arch_accel_class_init(ObjectClass *oc)
>  
>      object_class_property_set_description(oc, "eager-split-size",
>          "Eager Page Split chunk size for hugepages. (default: 0, disabled)");
> +
> +    object_class_property_add_str(oc, "pmu-filter",
> +                                  kvm_arch_get_pmu_filter,
> +                                  kvm_arch_set_pmu_filter);
> +
> +    object_class_property_set_description(oc, "pmu-filter",
> +        "PMU Event Filtering description for guest PMU. (default: NULL, 
> disabled)");
>  }
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index 3c175c93a7..0ed6744057 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -10,6 +10,7 @@
>   */
>  
>  #include "qemu/osdep.h"
> +#include <asm-arm64/kvm.h>
>  #include <sys/ioctl.h>
>  #include <sys/ptrace.h>
>  
> @@ -131,6 +132,77 @@ static bool kvm_arm_set_device_attr(CPUState *cs, struct 
> kvm_device_attr *attr,
>      return true;
>  }
>  
> +static void kvm_arm_pmu_filter_init(CPUState *cs)
> +{
> +    KVMState *kvm_state = cs->kvm_state;
> +    static bool pmu_filter_init = false;
> +    struct kvm_pmu_event_filter filter;
> +    struct kvm_device_attr attr = {
> +        .group      = KVM_ARM_VCPU_PMU_V3_CTRL,
> +        .attr       = KVM_ARM_VCPU_PMU_V3_FILTER,
> +        .addr       = (uint64_t)&filter,
> +    };
> +    char act;
> +    int i;
> +    gchar **event_filters;
> +
> +    if (!kvm_state->kvm_pmu_filter)
> +        return;
> +
> +    if (kvm_vcpu_ioctl(cs, KVM_HAS_DEVICE_ATTR, &attr)) {
> +        warn_report("The kernel doesn't support the PMU Event Filter!\n");
> +        return;
> +    }
> +
> +    /* The filter only needs to be initialized for 1 vcpu. */
Are you sure? This is a per vcpu device ctrl. Where is it written in the
doc that this shall not be called for each vcpu
> +    if (pmu_filter_init) {
> +        return;
> +    }
> +    pmu_filter_init = true;
> +
> +    event_filters = g_strsplit(kvm_state->kvm_pmu_filter, ";", -1);
> +
> +    for (i = 0; event_filters[i]; i++) {
> +        unsigned short start = 0, end = 0;
> +
> +        sscanf(event_filters[i], "%c:%hx-%hx", &act, &start, &end);
> +        if ((act != 'A' && act != 'D') || (!start && !end)) {
> +            warn_report("Skipping invalid PMU filter %s\n", 
> event_filters[i]);
> +            continue;
> +        }
> +
> +        filter = (struct kvm_pmu_event_filter) {
> +            .base_event     = start,
> +            .nevents        = end - start + 1,
> +            .action         = act == 'A' ? KVM_PMU_EVENT_ALLOW :
> +                                           KVM_PMU_EVENT_DENY,
> +        };
> +
> +        if (!kvm_arm_set_device_attr(cs, &attr, "PMU Event Filter")) {
> +            if (errno == EINVAL) {
> +                warn_report("Invalid PMU filter range [0x%x-0x%x]. "
> +                             "ARMv8.0 support 10 bits event space, "
> +                             "ARMv8.1 support 16 bits event space",
> +                             start, end);
> +            }
> +            else if (errno == ENODEV) {
> +                warn_report("GIC not initialized");
> +            }
> +            else if (errno == ENXIO) {
> +                warn_report("PMUv3 not properly configured or in-kernel 
> irqchip "
> +                            "not configured.");
> +            }
> +            else if (errno == EBUSY) {
> +                warn_report("PMUv3 already initialized or a VCPU has already 
> run");
> +            }
> +
> +            break;
> +        }
> +    }
> +
> +    g_strfreev(event_filters);
> +}
> +
>  void kvm_arm_pmu_init(CPUState *cs)
>  {
>      struct kvm_device_attr attr = {
> @@ -141,6 +213,9 @@ void kvm_arm_pmu_init(CPUState *cs)
>      if (!ARM_CPU(cs)->has_pmu) {
>          return;
>      }
> +
> +    kvm_arm_pmu_filter_init(cs);
> +
>      if (!kvm_arm_set_device_attr(cs, &attr, "PMU")) {
>          error_report("failed to init PMU");
>          abort();

Thanks

Eric




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