[3/5] i386/kvm: Support event with select & umask format in KVM PMU filter

Commit Message

Zhao Liu April 9, 2025, 8:26 a.m. UTC

The select&umask is the common way for x86 to identify the PMU event,
so support this way as the "x86-default" format in kvm-pmu-filter
object.

Signed-off-by: Zhao Liu <[e-mail]>
Tested-by: Yi Lai <[e-mail]>
---
Changes since RFC v2:
 * Drop hexadecimal variants and support numeric version in QAPI
   directly. (Daniel)
 * Rename "x86-default" format to "x86-select-umask". (Markus)
 * Add Tested-by from Yi.
 * Add documentation in qemu-options.hx.
 * QAPI style fix:
   - KVMPMU* stuff -> KvmPmu*.
 * Bump up the supported QAPI version to v10.1.

Changes since RFC v1:
 * Bump up the supported QAPI version to v10.0.
---
 accel/kvm/kvm-pmu.c      | 20 +++++++++++++++++++-
 include/system/kvm-pmu.h | 13 +++++++++++++
 qapi/kvm.json            | 21 +++++++++++++++++++--
 qemu-options.hx          |  3 +++
 target/i386/kvm/kvm.c    |  5 +++++
 5 files changed, 59 insertions(+), 3 deletions(-)

Patch

diff --git a/accel/kvm/kvm-pmu.c b/accel/kvm/kvm-pmu.c
index 22f749bf9183..fa73ef428e59 100644
--- a/accel/kvm/kvm-pmu.c
+++ b/accel/kvm/kvm-pmu.c
@@ -16,6 +16,8 @@ 
 #include "qom/object_interfaces.h"
 #include "system/kvm-pmu.h"
 
+#define UINT12_MAX (4095)
+
 static void kvm_pmu_filter_set_action(Object *obj, int value,
                                       Error **errp G_GNUC_UNUSED)
 {
@@ -53,9 +55,22 @@  static void kvm_pmu_filter_set_event(Object *obj, Visitor *v, const char *name,
     }
 
     for (node = head; node; node = node->next) {
-        switch (node->value->format) {
+        KvmPmuFilterEvent *event = node->value;
+
+        switch (event->format) {
         case KVM_PMU_EVENT_FORMAT_RAW:
             break;
+        case KVM_PMU_EVENT_FORMAT_X86_SELECT_UMASK: {
+            if (event->u.x86_select_umask.select > UINT12_MAX) {
+                error_setg(errp,
+                           "Parameter 'select' out of range (%d).",
+                           UINT12_MAX);
+                goto fail;
+            }
+
+            /* No need to check the range of umask since it's uint8_t. */
+            break;
+        }
         default:
             g_assert_not_reached();
         }
@@ -67,6 +82,9 @@  static void kvm_pmu_filter_set_event(Object *obj, Visitor *v, const char *name,
     filter->events = head;
     qapi_free_KvmPmuFilterEventList(old_head);
     return;
+
+fail:
+    qapi_free_KvmPmuFilterEventList(head);
 }
 
 static void kvm_pmu_filter_class_init(ObjectClass *oc, void *data)
diff --git a/include/system/kvm-pmu.h b/include/system/kvm-pmu.h
index 818fa309c191..6abc0d037aee 100644
--- a/include/system/kvm-pmu.h
+++ b/include/system/kvm-pmu.h
@@ -32,4 +32,17 @@  struct KVMPMUFilter {
     KvmPmuFilterEventList *events;
 };
 
+/*
+ * Stolen from Linux kernel (RAW_EVENT at tools/testing/selftests/kvm/include/
+ * x86_64/pmu.h).
+ *
+ * Encode an eventsel+umask pair into event-select MSR format.  Note, this is
+ * technically AMD's format, as Intel's format only supports 8 bits for the
+ * event selector, i.e. doesn't use bits 24:16 for the selector.  But, OR-ing
+ * in '0' is a nop and won't clobber the CMASK.
+ */
+#define X86_PMU_RAW_EVENT(eventsel, umask) (((eventsel & 0xf00UL) << 24) | \
+                                            ((eventsel) & 0xff) | \
+                                            ((umask) & 0xff) << 8)
+
 #endif /* KVM_PMU_H */
diff --git a/qapi/kvm.json b/qapi/kvm.json
index 1861d86a9726..cb151ca82e5c 100644
--- a/qapi/kvm.json
+++ b/qapi/kvm.json
@@ -36,10 +36,12 @@ 
 #
 # @raw: the encoded event code that KVM can directly consume.
 #
+# @x86-select-umask: standard x86 encoding format with select and umask.
+#
 # Since 10.1
 ##
 { 'enum': 'KvmPmuEventFormat',
-  'data': ['raw'] }
+  'data': ['raw', 'x86-select-umask'] }
 
 ##
 # @KvmPmuRawEvent:
@@ -54,6 +56,20 @@ 
 { 'struct': 'KvmPmuRawEvent',
   'data': { 'code': 'uint64' } }
 
+##
+# @KvmPmuX86SelectUmaskEvent:
+#
+# @select: x86 PMU event select field, which is a 12-bit unsigned
+#     number.
+#
+# @umask: x86 PMU event umask field.
+#
+# Since 10.1
+##
+{ 'struct': 'KvmPmuX86SelectUmaskEvent',
+  'data': { 'select': 'uint16',
+            'umask': 'uint8' } }
+
 ##
 # @KvmPmuFilterEvent:
 #
@@ -66,7 +82,8 @@ 
 { 'union': 'KvmPmuFilterEvent',
   'base': { 'format': 'KvmPmuEventFormat' },
   'discriminator': 'format',
-  'data': { 'raw': 'KvmPmuRawEvent' } }
+  'data': { 'raw': 'KvmPmuRawEvent',
+            'x86-select-umask': 'KvmPmuX86SelectUmaskEvent' } }
 
 ##
 # @KvmPmuFilterProperties:
diff --git a/qemu-options.hx b/qemu-options.hx
index 51a7c61ce0b0..5dcce067d8dd 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -6180,6 +6180,9 @@  SRST
              ((select) & 0xff) | \
              ((umask) & 0xff) << 8)
 
+        ``{"format":"x86-select-umask","select":event_select,"umask":event_umask}``
+            Specify the single x86 PMU event with select and umask fields.
+
         An example KVM PMU filter object would look like:
 
         .. parsed-literal::
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index fa3a696654cb..0d36ccf250ed 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -5974,6 +5974,10 @@  static bool kvm_config_pmu_event(KVMPMUFilter *filter,
         case KVM_PMU_EVENT_FORMAT_RAW:
             code = event->u.raw.code;
             break;
+        case KVM_PMU_EVENT_FORMAT_X86_SELECT_UMASK:
+            code = X86_PMU_RAW_EVENT(event->u.x86_select_umask.select,
+                                     event->u.x86_select_umask.umask);
+            break;
         default:
             g_assert_not_reached();
         }
@@ -6644,6 +6648,7 @@  static void kvm_arch_check_pmu_filter(const Object *obj, const char *name,
 
         switch (event->format) {
         case KVM_PMU_EVENT_FORMAT_RAW:
+        case KVM_PMU_EVENT_FORMAT_X86_SELECT_UMASK:
             break;
         default:
             error_setg(errp,