Hi Shaoqin,
On 1/15/24 09:01, 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).
do not hesitate to cc qemu-arm@xxxxxxxxxx for ARM specific topics.
Here is an example shows how to use the PMU Event Filtering, when
which shows
we launch a guest by use kvm, add such command line:
# qemu-system-aarch64 \
-accel kvm \
-cpu host,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).
Actually it filters it ;-) It would rather say this filters out the
cycle counter. But I am not a native speaker either ;-)
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.
do still work
Signed-off-by: Shaoqin Huang <shahuang@xxxxxxxxxx>
---
v4->v5:
- Change the kvm-pmu-filter as a -cpu sub-option. [Eric]
- Comment tweak. [Gavin]
- Rebase to the latest branch.
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]
docs/system/arm/cpu-features.rst | 23 ++++++++++
include/sysemu/kvm_int.h | 1 +
target/arm/cpu.h | 3 ++
target/arm/kvm.c | 78 ++++++++++++++++++++++++++++++++
4 files changed, 105 insertions(+)
diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst
index a5fb929243..44a797c50e 100644
--- a/docs/system/arm/cpu-features.rst
+++ b/docs/system/arm/cpu-features.rst
@@ -204,6 +204,29 @@ the list of KVM VCPU features and their descriptions.
the guest scheduler behavior and/or be exposed to the guest
userspace.
+``kvm-pmu-filter``
+ By default kvm-pmu-filter is disabled. This means that by default all pmu
+ events will be exposed to guest.
+
+ 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:
+
+ kvm-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 hexadecimal
+ format now. For example:
+
+ kvm-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
s/is/are
+ also allowed except the event 0x30 is denied, and all the other events
0x30 is/0x30 which is
+ are disallowed.
s/disallowed/denied just to match the above terminology.
+
TCG VCPU Features
=================
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;
I think this is not needed anymore
};
void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml,
diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 8c3ca2e231..1be7dca4aa 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -971,6 +971,9 @@ struct ArchCPU {
/* KVM steal time */
OnOffAuto kvm_steal_time;
+
+ /* KVM PMU Filter */
+ char *kvm_pmu_filter;
#endif /* CONFIG_KVM */
/* Uniprocessor system with MP extensions */
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index c5a3183843..413ee2720e 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -495,6 +495,22 @@ static void kvm_steal_time_set(Object *obj, bool value, Error **errp)
ARM_CPU(obj)->kvm_steal_time = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
}
+static char *kvm_pmu_filter_get(Object *obj, Error **errp)
+{
+ ARMCPU *cpu = ARM_CPU(obj);
+
+ return g_strdup(cpu->kvm_pmu_filter);
+}
+
+static void kvm_pmu_filter_set(Object *obj, const char *pmu_filter,
+ Error **errp)
+{
+ ARMCPU *cpu = ARM_CPU(obj);
+
+ g_free(cpu->kvm_pmu_filter);
+ cpu->kvm_pmu_filter = g_strdup(pmu_filter);
+}
+
/* KVM VCPU properties should be prefixed with "kvm-". */
void kvm_arm_add_vcpu_properties(ARMCPU *cpu)
{
@@ -516,6 +532,12 @@ 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)");
}
bool kvm_arm_pmu_supported(void)
@@ -1705,6 +1727,60 @@ 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;
+ gchar **event_filters;
wonder if you couldn't use g_auto(GStrv) event_filters with auto
cleenup? examples in qom/object.c for instance
+
+ 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!");
+ 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) {
I think I commented on that on the v4. Maybe I missed your reply. You
sure you don't need to call it for each vcpu?
+ 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;
+
+ sscanf(event_filters[i], "%c:%hx-%hx", &act, &start, &end);
+ if ((act != 'A' && act != 'D') || (!start && !end)) {
+ warn_report("Skipping invalid PMU filter %s", event_filters[i]);
+ continue;
+ }
+
+ 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 Event Filter")) {
Nit: maybe s/PMU Event Filter/PMU_V3_FILTER
+ break;
+ }
+ }
+
+ g_strfreev(event_filters);
+}
+
void kvm_arm_pmu_init(ARMCPU *cpu)
{
struct kvm_device_attr attr = {
@@ -1715,6 +1791,8 @@ void kvm_arm_pmu_init(ARMCPU *cpu)
if (!cpu->has_pmu) {
return;
}
+
+ kvm_arm_pmu_filter_init(cpu);
if (!kvm_arm_set_device_attr(cpu, &attr, "PMU")) {
error_report("failed to init PMU");
abort();
Along with this new vcpu feature you may want to add a test like what
was done in 68970d1e0d07 ("hw/arm/virt: Implement kvm-steal-time"), in
tests/qtest/arm-cpu-features.c
