Hi Shaoqin,
On 11/17/23 07:08, 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.
you remind the reader the default policy without filter (ie. expose all
events from the hots)
>
> 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 filter action defines if the whole
> event list is an allow or deny list, if the first filter action is "allow", all
> other events are denied except start-end; if the first filter action is "deny",
> all other events are allowed except start-end. For example:
I prefer the kernel doc wording
The first registered range defines the global policy (global ALLOW if
the first @action is DENY, global DENY if the first @action is ALLOW).
>
> pmu-filter="A:0x11-0x11;A:0x23-0x3a,D:0x30-0x30"
shoudn't the "," be replaced by a ";"?
I would add: since the first action is allow, we have a global deny policy.
>
> This 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 filter action is deny, we have a global allow policy.
this disables the filtering of the cycle counter (event 0x11 being
CPU_CYCLES)
kernel doc says that the ranges should match the PMU arch (10 bits on
ARMv8.0, 16 bits from ARMv8.1 onwards). How do you handle that?
>
> 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.
perf list should work as well
>
> Signed-off-by: Shaoqin Huang <shahuang@xxxxxxxxxx>
> ---
> v1->v2:
> - Add more description for allow and deny meaning in
> commit message. [Sebastian]
> - Small improvement. [Sebastian]
>
> v1: https://lore.kernel.org/all/20231113081713.153615-1-shahuang@xxxxxxxxxx/
> ---
> include/sysemu/kvm_int.h | 1 +
> qemu-options.hx | 16 +++++++++++++
> target/arm/kvm.c | 22 +++++++++++++++++
> target/arm/kvm64.c | 51 ++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 90 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..dd3518092c 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[;...] (KVM PMU Event Filter, default no filter. ARM only)\n"
> " 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 +260,21 @@ SRST
> impact on the memory. By default, this feature is disabled
> (eager-split-size=0).
>
> + ``pmu-filter={A,D}:start-end[;...]``
> + KVM implements pmu event filtering to prevent a guest from being able to
> + sample certain events. It has the following format:
> +
> + pmu-filter="{A,D}:start-end[;{A,D}:start-end...]"
you may add []* to express that you have any number of ranges
> +
> + The A means "allow" and D means "deny", start if the first event of the
> + range and the end is the last one. For example:
> +
> + pmu-filter="A:0x11-0x11;A:0x23-0x3a,D:0x30-0x30"
is is hex format only?
> +
> + This 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.
s/disallowed/hidden?
> +
> ``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..74796de055 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -1108,6 +1108,21 @@ 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);
> +
> + s->kvm_pmu_filter = g_strdup(pmu_filter);
can the user specify the option several times in which case we would
leak here?
> +}
> +
> void kvm_arch_accel_class_init(ObjectClass *oc)
> {
> object_class_property_add(oc, "eager-split-size", "size",
> @@ -1116,4 +1131,11 @@ 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..6eac328b48 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 +132,53 @@ 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)
> +{
> + 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,
> + };
> + KVMState *kvm_state = cs->kvm_state;
> + char *tmp;
> + char *str, act;
> +
> + if (!kvm_state->kvm_pmu_filter)
> + return;
> +
> + /* This only needs to be called for 1 vcpu. */
> + if (!pmu_filter_init)
> + pmu_filter_init = true;
where is it used?
> +
> + tmp = g_strdup(kvm_state->kvm_pmu_filter);
> +
> + for (str = strtok(tmp, ";"); str != NULL; str = strtok(NULL, ";")) {
> + unsigned short start = 0, end = 0;
> +
> + sscanf(str, "%c:%hx-%hx", &act, &start, &end);
> + if ((act != 'A' && act != 'D') || (!start && !end)) {
> + error_report("skipping invalid filter %s\n", str);
> + 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")) {
> + error_report("Failed to init PMU Event Filter\n");
you may add some hints about why this failed.
> + abort();
> + }
> + }
> +
> + g_free(tmp);
> +}
> +
> void kvm_arm_pmu_init(CPUState *cs)
> {
> struct kvm_device_attr attr = {
> @@ -141,6 +189,9 @@ 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();
I see x86 seems to have a similar capability (see
KVM_CAP_PMU_EVENT_FILTER). But I am not sure this is integrated in qemu?
Thanks
Eric
