[PATCH 0/2] RISC-V: KVM: Add PMU event filter support

[PATCH 0/2] RISC-V: KVM: Add PMU event filter support

[Yuhang.chen]

This series adds PMU event filter support to RISC-V KVM, allowing a
userspace VMM to restrict which SBI PMU events a guest is permitted to
program.

The KVM_SET_PMU_EVENT_FILTER ioctl and KVM_CAP_PMU_EVENT_FILTER already
exist as generic KVM uAPI (include/uapi/linux/kvm.h); RISC-V KVM does
not yet implement them.  Wiring them up lets a VMM limit a guest's PMU
event access, which is useful for sandboxing and for withholding host
PMU events the host does not intend to expose.

Patch 1 implements the kernel side: the uapi struct, the ioctl handler
with an SRCU-protected filter, enforcement in
kvm_riscv_vcpu_pmu_ctr_cfg_match() (a disallowed event fails with
SBI_ERR_NOT_SUPPORTED), and advertisement of KVM_CAP_PMU_EVENT_FILTER.

Patch 2 adds a selftest that covers the ALLOW/DENY semantics with the
event in and out of the list, filter clearing, and ioctl argument
rejection (EINVAL/E2BIG).

Testing: built and run under QEMU TCG with nested KVM (an L1 KVM host
running an L2 guest).  The selftest (patch 2) passes - all ALLOW/DENY
and argument-validation cases behave as expected - and dmesg stays
clean throughout the run.

Based on v7.2-rc2 (a635d6748234).

Assisted-by: YuanSheng:deepseek-v4-pro
Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Yuhang.chen <yhchen312@gmail.com>

Yuhang.chen (2):
  RISC-V: KVM: Add PMU event filter support
  RISC-V: KVM: selftests: Add PMU event filter test

 arch/riscv/include/asm/kvm_host.h             |   3 +
 arch/riscv/include/uapi/asm/kvm.h             |  20 ++
 arch/riscv/kvm/vcpu_pmu.c                     |  28 +++
 arch/riscv/kvm/vm.c                           |  66 +++++-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../kvm/riscv/pmu_event_filter_test.c         | 199 ++++++++++++++++++
 6 files changed, 316 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/kvm/riscv/pmu_event_filter_test.c

-- 
2.34.1

[PATCH 1/2] RISC-V: KVM: Add PMU event filter support

[Yuhang.chen]

Allow userspace to restrict which SBI PMU events a guest is permitted
to program via the new VM ioctl KVM_SET_PMU_EVENT_FILTER.  It takes a
struct kvm_pmu_event_filter whose events[] array holds SBI PMU event
indices encoded as (type << 16) | code.  The action field selects ALLOW
(only listed events may be programmed) or DENY (listed events are
rejected); nevents == 0 clears any active filter.

The filter is enforced in kvm_riscv_vcpu_pmu_ctr_cfg_match(), where a
disallowed event fails configuration with SBI_ERR_NOT_SUPPORTED.  It
governs new counter configuration only and is not retroactive.  The
filter lives in struct kvm_arch, read via SRCU on the vCPU run path and
replaced under kvm->lock with synchronize_srcu_expedited().

Advertise the feature with KVM_CAP_PMU_EVENT_FILTER.

Assisted-by: YuanSheng:deepseek-v4-pro
Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Yuhang.chen <yhchen312@gmail.com>
---
 arch/riscv/include/asm/kvm_host.h |  3 ++
 arch/riscv/include/uapi/asm/kvm.h | 20 ++++++++++
 arch/riscv/kvm/vcpu_pmu.c         | 28 +++++++++++++
 arch/riscv/kvm/vm.c               | 66 ++++++++++++++++++++++++++++++-
 4 files changed, 116 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index 60017ceec9d2..1cd3d6a11057 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -95,6 +95,9 @@ struct kvm_arch {
 
 	/* KVM_CAP_RISCV_MP_STATE_RESET */
 	bool mp_state_reset;
+
+	/* KVM_SET_PMU_EVENT_FILTER */
+	struct kvm_pmu_event_filter __rcu *pmu_event_filter;
 };
 
 struct kvm_cpu_trap {
diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index 504e73305343..da4f639fa89f 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -12,6 +12,7 @@
 #ifndef __ASSEMBLER__
 
 #include <linux/types.h>
+#include <linux/stddef.h>
 #include <asm/bitsperlong.h>
 #include <asm/ptrace.h>
 
@@ -396,6 +397,25 @@ struct kvm_riscv_sbi_fwft {
 /* One single KVM irqchip, ie. the AIA */
 #define KVM_NR_IRQCHIPS			1
 
+/* for KVM_CAP_PMU_EVENT_FILTER */
+#define KVM_PMU_EVENT_ALLOW	0
+#define KVM_PMU_EVENT_DENY	1
+
+/*
+ * For KVM_SET_PMU_EVENT_FILTER: restrict which SBI PMU events a guest may
+ * configure.  Each @events entry is a SBI PMU event index (type in bits
+ * 19:16, code in bits 15:0).  %KVM_PMU_EVENT_ALLOW permits only listed
+ * events; %KVM_PMU_EVENT_DENY rejects them.  Enforced at counter
+ * configuration (SBI PMU COUNTER_CFG_MATCH), not retroactively.
+ */
+struct kvm_pmu_event_filter {
+	__u32 action;
+	__u32 nevents;
+	__u32 flags;
+	__u32 pad;
+	__DECLARE_FLEX_ARRAY(__u64, events);
+};
+
 #endif
 
 #endif /* __LINUX_KVM_RISCV_H */
diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
index bb46dcbfb24d..bc7d297a63ce 100644
--- a/arch/riscv/kvm/vcpu_pmu.c
+++ b/arch/riscv/kvm/vcpu_pmu.c
@@ -733,6 +733,29 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
 	return 0;
 }
 
+static bool kvm_riscv_pmu_event_allowed(struct kvm *kvm, unsigned long eidx)
+{
+	struct kvm_pmu_event_filter *filter;
+	bool in_list = false;
+	unsigned int i;
+
+	filter = srcu_dereference(kvm->arch.pmu_event_filter, &kvm->srcu);
+	if (!filter)
+		return true;
+
+	for (i = 0; i < filter->nevents; i++) {
+		if ((unsigned long)filter->events[i] == eidx) {
+			in_list = true;
+			break;
+		}
+	}
+
+	/* ALLOW: permit only listed events; DENY: reject them. */
+	if (filter->action == KVM_PMU_EVENT_ALLOW)
+		return in_list;
+	return !in_list;
+}
+
 int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_base,
 				     unsigned long ctr_mask, unsigned long flags,
 				     unsigned long eidx, u64 evtdata,
@@ -773,6 +796,11 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
 		goto out;
 	}
 
+	if (!kvm_riscv_pmu_event_allowed(vcpu->kvm, eidx)) {
+		sbiret = SBI_ERR_NOT_SUPPORTED;
+		goto out;
+	}
+
 	/*
 	 * SKIP_MATCH flag indicates the caller is aware of the assigned counter
 	 * for this event. Just do a sanity check if it already marked used.
diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
index a9f083feeb76..6f822c43f156 100644
--- a/arch/riscv/kvm/vm.c
+++ b/arch/riscv/kvm/vm.c
@@ -53,6 +53,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 {
 	kvm_destroy_vcpus(kvm);
 
+	kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
+
 	kvm_riscv_aia_destroy_vm(kvm);
 }
 
@@ -187,6 +189,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_MP_STATE:
 	case KVM_CAP_IMMEDIATE_EXIT:
 	case KVM_CAP_SET_GUEST_DEBUG:
+	case KVM_CAP_PMU_EVENT_FILTER:
 		r = 1;
 		break;
 	case KVM_CAP_NR_VCPUS:
@@ -265,7 +268,68 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
 	}
 }
 
+#define KVM_PMU_EVENT_FILTER_MAX_EVENTS	256
+
+static int kvm_riscv_vm_ioctl_set_pmu_event_filter(struct kvm *kvm,
+						   void __user *argp)
+{
+	struct kvm_pmu_event_filter __user *user_filter = argp;
+	struct kvm_pmu_event_filter *filter, tmp;
+	size_t size;
+	int r = 0;
+
+	if (copy_from_user(&tmp, user_filter, sizeof(tmp)))
+		return -EFAULT;
+
+	if (tmp.action != KVM_PMU_EVENT_ALLOW &&
+	    tmp.action != KVM_PMU_EVENT_DENY)
+		return -EINVAL;
+
+	if (tmp.flags)
+		return -EINVAL;
+
+	if (tmp.nevents > KVM_PMU_EVENT_FILTER_MAX_EVENTS)
+		return -E2BIG;
+
+	size = struct_size(filter, events, tmp.nevents);
+	filter = kzalloc(size, GFP_KERNEL_ACCOUNT);
+	if (!filter)
+		return -ENOMEM;
+
+	filter->action = tmp.action;
+	filter->nevents = tmp.nevents;
+	filter->flags = tmp.flags;
+
+	if (copy_from_user(filter->events, user_filter->events,
+			   flex_array_size(filter, events, filter->nevents))) {
+		r = -EFAULT;
+		goto cleanup;
+	}
+
+	mutex_lock(&kvm->lock);
+	filter = rcu_replace_pointer(kvm->arch.pmu_event_filter, filter,
+				     mutex_is_locked(&kvm->lock));
+	mutex_unlock(&kvm->lock);
+	synchronize_srcu_expedited(&kvm->srcu);
+
+cleanup:
+	kfree(filter);
+	return r;
+}
+
 int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 {
-	return -EINVAL;
+	struct kvm *kvm = filp->private_data;
+	void __user *argp = (void __user *)arg;
+	int r;
+
+	switch (ioctl) {
+	case KVM_SET_PMU_EVENT_FILTER:
+		r = kvm_riscv_vm_ioctl_set_pmu_event_filter(kvm, argp);
+		break;
+	default:
+		r = -EINVAL;
+	}
+
+	return r;
 }
-- 
2.34.1

Re: [PATCH 1/2] RISC-V: KVM: Add PMU event filter support

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] Guest can trivially bypass PMU event DENY filters by setting unmasked high bits in the event index (eidx).
- [Medium] RISC-V defines a structurally incompatible `struct kvm_pmu_event_filter` compared to x86, which causes the KVM_SET_PMU_EVENT_FILTER ioctl number to diverge and breaks cross-architecture userspace code.
- [Medium] Missing validation for the UAPI padding field prevents safe future extensions.
--

--- Patch [1]: [PATCH 1/2] RISC-V: KVM: Add PMU event filter support ---
commit 4331081d868d3aa2c618439fb21772bb580c0495
Author: Yuhang.chen <yhchen312@gmail.com>

RISC-V: KVM: Add PMU event filter support
    
Allow userspace to restrict which SBI PMU events a guest is permitted
to program via the new VM ioctl KVM_SET_PMU_EVENT_FILTER.  It takes a
struct kvm_pmu_event_filter whose events[] array holds SBI PMU event
indices encoded as (type << 16) | code.

> diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> index 504e73305343a..da4f639fa89f8 100644
> --- a/arch/riscv/include/uapi/asm/kvm.h
> +++ b/arch/riscv/include/uapi/asm/kvm.h
[ ... ]
> @@ -396,6 +397,25 @@ struct kvm_riscv_sbi_fwft {
>  /* One single KVM irqchip, ie. the AIA */
>  #define KVM_NR_IRQCHIPS			1
>  
> +/* for KVM_CAP_PMU_EVENT_FILTER */
> +#define KVM_PMU_EVENT_ALLOW	0
> +#define KVM_PMU_EVENT_DENY	1
> +
> +/*
> + * For KVM_SET_PMU_EVENT_FILTER: restrict which SBI PMU events a guest may
> + * configure.  Each @events entry is a SBI PMU event index (type in bits
> + * 19:16, code in bits 15:0).  %KVM_PMU_EVENT_ALLOW permits only listed
> + * events; %KVM_PMU_EVENT_DENY rejects them.  Enforced at counter
> + * configuration (SBI PMU COUNTER_CFG_MATCH), not retroactively.
> + */
> +struct kvm_pmu_event_filter {
> +	__u32 action;
> +	__u32 nevents;
> +	__u32 flags;
> +	__u32 pad;
> +	__DECLARE_FLEX_ARRAY(__u64, events);
> +};

[Severity: Medium]
Since KVM_SET_PMU_EVENT_FILTER is a generic KVM ioctl, does defining
struct kvm_pmu_event_filter with a different size and layout than the existing
x86 definition break cross-architecture userspace code? 

The size difference (due to missing fields like fixed_counter_bitmap and
different padding) causes the ioctl number to evaluate to a different numeric
value on RISC-V. Could this be unified with the existing generic definition to
maintain KVM UAPI consistency?

>  #endif
>  
>  #endif /* __LINUX_KVM_RISCV_H */
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index 2025b664961c8..189650b04c37d 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
[ ... ]
> @@ -733,6 +733,29 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
>  	return 0;
>  }
>  
> +static bool kvm_riscv_pmu_event_allowed(struct kvm *kvm, unsigned long eidx)
> +{
> +	struct kvm_pmu_event_filter *filter;
> +	bool in_list = false;
> +	unsigned int i;
> +
> +	filter = srcu_dereference(kvm->arch.pmu_event_filter, &kvm->srcu);
> +	if (!filter)
> +		return true;
> +
> +	for (i = 0; i < filter->nevents; i++) {
> +		if ((unsigned long)filter->events[i] == eidx) {
> +			in_list = true;
> +			break;
> +		}
> +	}

[Severity: High]
Can a malicious guest bypass the DENY filter by setting high unmasked bits
in the event index?

In kvm_riscv_pmu_event_allowed(), the guest-controlled eidx is exact-matched
against the filter entries. If the guest provides an eidx with bits above
bit 19 set (e.g., bit 63), the equality check fails and a DENY filter will
incorrectly allow it.

Because the subsequent configuration logic masks out the high bits using
get_event_type() and get_event_code(), the blocked event is still
successfully configured. Should eidx be properly masked before it is compared
against the filter events?

> +
> +	/* ALLOW: permit only listed events; DENY: reject them. */
> +	if (filter->action == KVM_PMU_EVENT_ALLOW)
> +		return in_list;
> +	return !in_list;
> +}
> +
> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> index a9f083feeb767..6f822c43f1569 100644
> --- a/arch/riscv/kvm/vm.c
> +++ b/arch/riscv/kvm/vm.c
[ ... ]
> @@ -265,7 +268,68 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>  	}
>  }
>  
> +#define KVM_PMU_EVENT_FILTER_MAX_EVENTS	256
> +
> +static int kvm_riscv_vm_ioctl_set_pmu_event_filter(struct kvm *kvm,
> +						   void __user *argp)
> +{
> +	struct kvm_pmu_event_filter __user *user_filter = argp;
> +	struct kvm_pmu_event_filter *filter, tmp;
> +	size_t size;
> +	int r = 0;
> +
> +	if (copy_from_user(&tmp, user_filter, sizeof(tmp)))
> +		return -EFAULT;
> +
> +	if (tmp.action != KVM_PMU_EVENT_ALLOW &&
> +	    tmp.action != KVM_PMU_EVENT_DENY)
> +		return -EINVAL;
> +
> +	if (tmp.flags)
> +		return -EINVAL;
> +
> +	if (tmp.nevents > KVM_PMU_EVENT_FILTER_MAX_EVENTS)
> +		return -E2BIG;

[Severity: Medium]
Does this code leave the tmp.pad field unvalidated?

If userspace passes uninitialized data or garbage in the padding field,
the kernel will silently accept it because there is no check ensuring
tmp.pad is zero. Will this prevent safely repurposing the padding field
for new features or flags in the future without breaking ABI compatibility
for existing applications?

> +
> +	size = struct_size(filter, events, tmp.nevents);
> +	filter = kzalloc(size, GFP_KERNEL_ACCOUNT);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260807035039.294998-1-yhchen312@gmail.com?part=1

[PATCH 2/2] RISC-V: KVM: selftests: Add PMU event filter test

[Yuhang.chen]

Add a selftest that exercises KVM_SET_PMU_EVENT_FILTER on RISC-V. The
guest programs the CPU cycles and instructions SBI PMU events through
SBI_EXT_PMU_COUNTER_CFG_MATCH while the host installs filters with the
ALLOW and DENY actions, asserting that disallowed events return
SBI_ERR_NOT_SUPPORTED and allowed events succeed.

The test also validates ioctl argument rejection: an invalid action, a
non-zero flags field, and an over-large nevents value are each expected
to fail with -EINVAL or -E2BIG. A baseline run verifies PMU
availability and the test skips (KSFT_SKIP) when PMU or the filter
capability is absent.

Assisted-by: YuanSheng:deepseek-v4-pro
Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Yuhang.chen <yhchen312@gmail.com>
---
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../kvm/riscv/pmu_event_filter_test.c         | 199 ++++++++++++++++++
 2 files changed, 200 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/riscv/pmu_event_filter_test.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index d28a057fa6c2..5d2dc3b25eac 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -218,6 +218,7 @@ TEST_GEN_PROGS_s390 += pre_fault_memory_test
 TEST_GEN_PROGS_riscv = $(TEST_GEN_PROGS_COMMON)
 TEST_GEN_PROGS_riscv += riscv/sbi_pmu_test
 TEST_GEN_PROGS_riscv += riscv/ebreak_test
+TEST_GEN_PROGS_riscv += riscv/pmu_event_filter_test
 TEST_GEN_PROGS_riscv += access_tracking_perf_test
 TEST_GEN_PROGS_riscv += arch_timer
 TEST_GEN_PROGS_riscv += coalesced_io_test
diff --git a/tools/testing/selftests/kvm/riscv/pmu_event_filter_test.c b/tools/testing/selftests/kvm/riscv/pmu_event_filter_test.c
new file mode 100644
index 000000000000..1a76fce2aca6
--- /dev/null
+++ b/tools/testing/selftests/kvm/riscv/pmu_event_filter_test.c
@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test for RISC-V KVM_SET_PMU_EVENT_FILTER.
+ *
+ * Verify that a VM-scoped PMU event filter installed via the
+ * KVM_SET_PMU_EVENT_FILTER ioctl is enforced when a guest configures a
+ * counter through the SBI PMU COUNTER_CFG_MATCH call:
+ *
+ *   - with no filter, events are programmable (baseline / PMU probe);
+ *   - KVM_PMU_EVENT_DENY rejects the listed events;
+ *   - KVM_PMU_EVENT_ALLOW admits only the listed events;
+ *   - replacing the filter with an empty DENY list re-enables everything.
+ *
+ * The filter is checked before any perf event is created, so the test only
+ * ever programs the cycle event (always supported by the host PMU) and varies
+ * the filter *list* contents to exercise membership without depending on host
+ * support for other events.  Counter management and SBI error reporting happen
+ * in the guest; the host installs filters and checks the reported errors.
+ */
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "kvm_util.h"
+#include "test_util.h"
+#include "processor.h"
+#include "ucall_common.h"
+#include "sbi.h"
+
+/* SBI PMU hardware event indexes (type == HW == 0, so eidx == code). */
+#define EV_CYCLES	SBI_PMU_HW_CPU_CYCLES		/* 1 */
+#define EV_INSTR	SBI_PMU_HW_INSTRUCTIONS		/* 2 */
+
+/* Must match KVM_PMU_EVENT_FILTER_MAX_EVENTS in arch/riscv/kvm/vm.c. */
+#define MAX_EVENTS	256
+
+static void guest_code(void)
+{
+	struct sbiret ret;
+	unsigned long ctr;
+	long err;
+
+	for (;;) {
+		/*
+		 * Request the fixed cycle counter (cbase=0, cmask=1) for the
+		 * cycle event.  The host installs (or clears) the filter
+		 * before each entry, so the result reflects the active policy.
+		 */
+		ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_CFG_MATCH,
+				0, 1, 0, EV_CYCLES, 0, 0);
+		err = ret.error;
+		ctr = ret.value;
+
+		/* Release the counter on success so the next iteration reuses it. */
+		if (!err)
+			sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP,
+				  ctr, 1, SBI_PMU_STOP_FLAG_RESET, 0, 0, 0);
+
+		GUEST_SYNC1(err);
+	}
+}
+
+static struct kvm_pmu_event_filter *
+build_filter(__u32 action, __u32 flags, const __u64 *events, __u32 nevents)
+{
+	struct kvm_pmu_event_filter *f;
+	size_t size = sizeof(*f) + (size_t)nevents * sizeof(__u64);
+
+	f = calloc(1, size);
+	TEST_ASSERT(f, "calloc(pmu_event_filter)");
+	f->action = action;
+	f->nevents = nevents;
+	f->flags = flags;
+	if (nevents && events)
+		memcpy(f->events, events, nevents * sizeof(__u64));
+	return f;
+}
+
+/* Install a filter, asserting success. */
+static void set_filter(struct kvm_vm *vm, __u32 action,
+		       const __u64 *events, __u32 nevents)
+{
+	struct kvm_pmu_event_filter *f = build_filter(action, 0, events, nevents);
+
+	vm_ioctl(vm, KVM_SET_PMU_EVENT_FILTER, f);
+	free(f);
+}
+
+/* Install a filter and return the raw ioctl result (for negative tests). */
+static int try_set_filter(struct kvm_vm *vm, __u32 action, __u32 flags,
+			  const __u64 *events, __u32 nevents)
+{
+	struct kvm_pmu_event_filter *f = build_filter(action, flags, events, nevents);
+	int ret = __vm_ioctl(vm, KVM_SET_PMU_EVENT_FILTER, f);
+
+	free(f);
+	return ret;
+}
+
+/* Run the guest one step and return the cfg_match error code it reports. */
+static long run_one(struct kvm_vcpu *vcpu)
+{
+	struct ucall uc;
+
+	vcpu_run(vcpu);
+	TEST_ASSERT_EQ(get_ucall(vcpu, &uc), UCALL_SYNC);
+	return (long)uc.args[0];
+}
+
+static void test_filter_case(struct kvm_vm *vm, struct kvm_vcpu *vcpu,
+			     __u32 action, const __u64 *events, __u32 nevents,
+			     long expect, const char *desc)
+{
+	long err;
+
+	set_filter(vm, action, events, nevents);
+	err = run_one(vcpu);
+	TEST_ASSERT_EQ(err, expect);
+	pr_info("%s: err=%ld (expected %ld)\n", desc, err, expect);
+}
+
+static void test_bad_args(struct kvm_vm *vm)
+{
+	__u64 ev = EV_CYCLES;
+	int ret;
+
+	/* Invalid action. */
+	errno = 0;
+	ret = try_set_filter(vm, 2, 0, &ev, 1);
+	TEST_ASSERT(ret < 0 && errno == EINVAL,
+		    "invalid action should fail with EINVAL, got ret=%d errno=%d",
+		    ret, errno);
+
+	/* Non-zero flags are not supported. */
+	errno = 0;
+	ret = try_set_filter(vm, KVM_PMU_EVENT_ALLOW, 1, &ev, 1);
+	TEST_ASSERT(ret < 0 && errno == EINVAL,
+		    "non-zero flags should fail with EINVAL, got ret=%d errno=%d",
+		    ret, errno);
+
+	/* Too many events. */
+	errno = 0;
+	ret = try_set_filter(vm, KVM_PMU_EVENT_DENY, 0, NULL, MAX_EVENTS + 1);
+	TEST_ASSERT(ret < 0 && errno == E2BIG,
+		    "nevents > max should fail with E2BIG, got ret=%d errno=%d",
+		    ret, errno);
+}
+
+int main(void)
+{
+	struct kvm_vm *vm;
+	struct kvm_vcpu *vcpu;
+	long err;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_PMU_EVENT_FILTER));
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
+	/*
+	 * Baseline / PMU probe: with no filter the cycle event must be
+	 * programmable.  If it isn't, the host PMU is unusable in this
+	 * environment (e.g. Sscofpmf unavailable under TCG); skip the rest.
+	 */
+	err = run_one(vcpu);
+	if (err) {
+		pr_info("PMU unavailable (baseline cfg_match err=%ld), skipping\n",
+			err);
+		kvm_vm_free(vm);
+		exit(KSFT_SKIP);
+	}
+
+	/* DENY{cycles}: the cycle event is rejected. */
+	test_filter_case(vm, vcpu, KVM_PMU_EVENT_DENY,
+			 &(__u64){ EV_CYCLES }, 1,
+			 SBI_ERR_NOT_SUPPORTED, "deny cycles");
+
+	/* ALLOW{cycles}: the cycle event is admitted. */
+	test_filter_case(vm, vcpu, KVM_PMU_EVENT_ALLOW,
+			 &(__u64){ EV_CYCLES }, 1,
+			 0, "allow cycles");
+
+	/*
+	 * ALLOW{instructions}: cycles is not in the allow list, so it is
+	 * rejected.  Instructions itself is never programmed, so host support
+	 * for it is irrelevant.
+	 */
+	test_filter_case(vm, vcpu, KVM_PMU_EVENT_ALLOW,
+			 &(__u64){ EV_INSTR }, 1,
+			 SBI_ERR_NOT_SUPPORTED, "cycles not in allow{instr}");
+
+	/* Empty DENY list: nothing is denied, cycles is programmable again. */
+	test_filter_case(vm, vcpu, KVM_PMU_EVENT_DENY, NULL, 0,
+			 0, "clear (deny empty)");
+
+	test_bad_args(vm);
+
+	kvm_vm_free(vm);
+	return 0;
+}
-- 
2.34.1