[Patch v3 5/6] perf tools kvm: Use "cycles" to sample guest for "kvm record" on Intel

Dapeng Mi
2025-09-19T02:18:52Z

After KVM supports PEBS for guest on Intel platforms
(https://lore.kernel.org/all/20220411101946.20262-1-likexu@tencent.com/),
host loses the capability to sample guest with PEBS since all PEBS related
MSRs are switched to guest value after vm-entry, like IA32_DS_AREA MSR is
switched to guest GVA at vm-entry. This would lead to "perf kvm record"
fails to sample guest on Intel platforms since "cycles:P" event is used to
sample guest by default as below case shows.

sudo perf kvm record -a
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.787 MB perf.data.guest ]

So to ensure guest record can be sampled successfully, use "cycles"
instead of "cycles:P" to sample guest record by default on Intel
platforms. With this patch, the guest record can be sampled
successfully.

sudo perf kvm record -a
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.783 MB perf.data.guest (23 samples) ]

Reported-by: Kevin Tian <kevin.tian@intel.com>
Fixes: cf8e55fe50df ("KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64")
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/arch/x86/util/kvm-stat.c | 51 +++++++++++++++++++++++++++++
tools/perf/builtin-kvm.c | 10 ------
tools/perf/util/kvm-stat.h | 10 ++++++
3 files changed, 61 insertions(+), 10 deletions(-)

diff --git a/tools/perf/arch/x86/util/kvm-stat.c b/tools/perf/arch/x86/util/kvm-stat.c
index 424716518b75..bff36f9345ea 100644
--- a/tools/perf/arch/x86/util/kvm-stat.c
+++ b/tools/perf/arch/x86/util/kvm-stat.c
@@ -3,9 +3,11 @@
#include <string.h>
#include "../../../util/kvm-stat.h"
#include "../../../util/evsel.h"
+#include "../../../util/env.h"
#include <asm/svm.h>
#include <asm/vmx.h>
#include <asm/kvm.h>
+#include <subcmd/parse-options.h>

define_exit_reasons_table(vmx_exit_reasons, VMX_EXIT_REASONS);
define_exit_reasons_table(svm_exit_reasons, SVM_EXIT_REASONS);
@@ -211,3 +213,52 @@ int cpu_isa_init(struct perf_kvm_stat *kvm, const char *cpuid)

return 0;
}
+
+/*
+ * After KVM supports PEBS for guest on Intel platforms
+ * (https://lore.kernel.org/all/20220411101946.20262-1-likexu@tencent.com/),
+ * host loses the capability to sample guest with PEBS since all PEBS related
+ * MSRs are switched to guest value after vm-entry, like IA32_DS_AREA MSR is
+ * switched to guest GVA at vm-entry. This would lead to "perf kvm record"
+ * fails to sample guest on Intel platforms since "cycles:P" event is used to
+ * sample guest by default.
+ *
+ * So, to avoid this issue explicitly use "cycles" instead of "cycles:P" event
+ * by default to sample guest on Intel platforms.
+ */
+int kvm_add_default_arch_event(int *argc, const char **argv)
+{
+ const char **tmp;
+ bool event = false;
+ int ret = 0, i, j = *argc;
+
+ const struct option event_options[] = {
+ OPT_BOOLEAN('e', "event", &event, NULL),
+ OPT_BOOLEAN(0, "pfm-events", &event, NULL),
+ OPT_END()
+ };
+
+ if (!x86__is_intel_cpu())
+ return 0;
+
+ tmp = calloc(j + 1, sizeof(char *));
+ if (!tmp)
+ return -ENOMEM;
+
+ for (i = 0; i < j; i++)
+ tmp[i] = argv[i];
+
+ parse_options(j, tmp, event_options, NULL, PARSE_OPT_KEEP_UNKNOWN);
+ if (!event) {
+ argv[j++] = STRDUP_FAIL_EXIT("-e");
+ argv[j++] = STRDUP_FAIL_EXIT("cycles");
+ *argc += 2;
+ }
+
+ free(tmp);
+ return 0;
+
+EXIT:
+ free(tmp);
+ return ret;
+}
diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
index d297a7b2c088..c0d62add4996 100644
--- a/tools/perf/builtin-kvm.c
+++ b/tools/perf/builtin-kvm.c
@@ -1636,16 +1636,6 @@ static int kvm_events_report_vcpu(struct perf_kvm_stat *kvm)
return ret;
}

-#define STRDUP_FAIL_EXIT(s) \
- ({ char *_p; \
- _p = strdup(s); \
- if (!_p) { \
- ret = -ENOMEM; \
- goto EXIT; \
- } \
- _p; \
- })
-
int __weak setup_kvm_events_tp(struct perf_kvm_stat *kvm __maybe_unused)
{
return 0;
diff --git a/tools/perf/util/kvm-stat.h b/tools/perf/util/kvm-stat.h
index 4249542544bb..53db3d56108b 100644
--- a/tools/perf/util/kvm-stat.h
+++ b/tools/perf/util/kvm-stat.h
@@ -190,5 +190,15 @@ static inline struct kvm_info *kvm_info__new(void)
#define kvm_info__zput(ki) do { } while (0)
#endif /* HAVE_KVM_STAT_SUPPORT */

+#define STRDUP_FAIL_EXIT(s) \
+ ({ char *_p; \
+ _p = strdup(s); \
+ if (!_p) { \
+ ret = -ENOMEM; \
+ goto EXIT; \
+ } \
+ _p; \
+ })
+
extern int kvm_add_default_arch_event(int *argc, const char **argv);
#endif /* __PERF_KVM_STAT_H */
--
2.34.1