On Wed, Feb 21, 2024 at 01:34:31AM -0500, Shaoqin Huang wrote:
> The KVM_ARM_VCPU_PMU_V3_FILTER provides the ability to let the VMM decide
> which PMU events are provided to the guest. Add a new option
> `kvm-pmu-filter` as -cpu sub-option to set the PMU Event Filtering.
> Without the filter, all PMU events are exposed from host to guest by
> default. The usage of the new sub-option can be found from the updated
> document (docs/system/arm/cpu-features.rst).
>
> Here is an example which 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 \
> -cpu host,kvm-pmu-filter="D:0x11-0x11"
snip
> @@ -517,6 +533,12 @@ void kvm_arm_add_vcpu_properties(ARMCPU *cpu)
> kvm_steal_time_set);
> object_property_set_description(obj, "kvm-steal-time",
> "Set off to disable KVM steal time.");
> +
> + object_property_add_str(obj, "kvm-pmu-filter", kvm_pmu_filter_get,
> + kvm_pmu_filter_set);
> + object_property_set_description(obj, "kvm-pmu-filter",
> + "PMU Event Filtering description for "
> + "guest PMU. (default: NULL, disabled)");
> }
Passing a string property, but....[1]
>
> bool kvm_arm_pmu_supported(void)
> @@ -1706,6 +1728,62 @@ static bool kvm_arm_set_device_attr(ARMCPU *cpu, struct kvm_device_attr *attr,
> return true;
> }
>
> +static void kvm_arm_pmu_filter_init(ARMCPU *cpu)
> +{
> + static bool pmu_filter_init;
> + 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,
> + };
> + int i;
> + g_auto(GStrv) event_filters;
> +
> + if (!cpu->kvm_pmu_filter) {
> + return;
> + }
> + if (kvm_vcpu_ioctl(CPU(cpu), KVM_HAS_DEVICE_ATTR, &attr)) {
> + warn_report("The KVM doesn't support the PMU Event Filter!");
If the user requested a filter and it can't be supported, QEMU
must exit with an error, not ignore the user's request.
> + return;
> + }
> +
> + /*
> + * The filter only needs to be initialized through one vcpu ioctl and it
> + * will affect all other vcpu in the vm.
> + */
> + if (pmu_filter_init) {
> + return;
> + } else {
> + pmu_filter_init = true;
> + }
> +
> + event_filters = g_strsplit(cpu->kvm_pmu_filter, ";", -1);
> + for (i = 0; event_filters[i]; i++) {
> + unsigned short start = 0, end = 0;
> + char act;
> +
> + if (sscanf(event_filters[i], "%c:%hx-%hx", &act, &start, &end) != 3) {
> + warn_report("Skipping invalid PMU filter %s", event_filters[i]);
> + continue;
Warning on user syntax errors is undesirable - it should be a fatal
error of the user gets this wrong.
> + }
> +
> + if ((act != 'A' && act != 'D') || start > end) {
> + warn_report("Skipping invalid PMU filter %s", event_filters[i]);
> + continue;
Likewise should be fatal.
> + }
> +
> + filter.base_event = start;
> + filter.nevents = end - start + 1;
> + filter.action = (act == 'A') ? KVM_PMU_EVENT_ALLOW :
> + KVM_PMU_EVENT_DENY;
> +
> + if (!kvm_arm_set_device_attr(cpu, &attr, "PMU_V3_FILTER")) {
> + break;
> + }
> + }
> +}
..[1] then implementing a custom parser is rather a QEMU design anti-pattern,
especially when the proposed syntax is incapable of being mapped into the
normal QAPI syntax for a list of structs should we want to fully convert
-cpu to QAPI parsing later. I wonder if can we model this property with
QAPI now ?
With regards,
Daniel
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