linux-kernel - [PATCH 1/1] KVM: x86: Print names of apicv inhibit reasons in traces

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Message-Id: <20240214223554.1033154-1-alejandro.j.jimenez@oracle.com>
Date: Wed, 14 Feb 2024 22:35:54 +0000
From: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
To: kvm@...r.kernel.org
Cc: seanjc@...gle.com, pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        joao.m.martins@...cle.com, boris.ostrovsky@...cle.com,
        suravee.suthikulpanit@....com, mlevitsk@...hat.com,
        alejandro.j.jimenez@...cle.com
Subject: [PATCH 1/1] KVM: x86: Print names of apicv inhibit reasons in traces

Use the tracing infrastructure helper __print_flags() for printing flag
bitfields, to enhance the trace output by displaying a string describing
each of the inhibit reasons set.

The kvm_apicv_inhibit_changed tracepoint currently shows the raw bitmap
value, requiring the user to consult the source file where the inhbit
reasons are defined to decode the trace output.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>

---
checkpatch reports an error:
ERROR: Macros with complex values should be enclosed in parentheses

but that seems common for other patches that also use a macro to define an array
of struct trace_print_flags used by __print_flags().

I did not include an example of the new traces in the commit message since they
are longer than 80 columns, but perhaps that is desirable. e.g.:

qemu-system-x86-6961    [055] .....  1779.344065: kvm_apicv_inhibit_changed: set reason=2, inhibits=0x4 ABSENT
qemu-system-x86-6961    [055] .....  1779.356710: kvm_apicv_inhibit_changed: cleared reason=2, inhibits=0x0

qemu-system-x86-9912    [137] ..... 57106.196107: kvm_apicv_inhibit_changed: set reason=8, inhibits=0x300 IRQWIN|PIT_REINJ
qemu-system-x86-9912    [137] ..... 57106.196115: kvm_apicv_inhibit_changed: cleared reason=8, inhibits=0x200 PIT_REINJ
---
 arch/x86/kvm/trace.h | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index b82e6ed4f024..8469e59dfce2 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -1372,6 +1372,27 @@ TRACE_EVENT(kvm_hv_stimer_cleanup,
 		  __entry->vcpu_id, __entry->timer_index)
 );
 
+/*
+ * The inhibit flags in this flag array must be kept in sync with the
+ * kvm_apicv_inhibit enum members in <asm/kvm_host.h>.
+ */
+#define APICV_INHIBIT_FLAGS \
+	{ BIT(APICV_INHIBIT_REASON_DISABLE),		 "DISABLED" }, \
+	{ BIT(APICV_INHIBIT_REASON_HYPERV),		 "HYPERV" }, \
+	{ BIT(APICV_INHIBIT_REASON_ABSENT),		 "ABSENT" }, \
+	{ BIT(APICV_INHIBIT_REASON_BLOCKIRQ),		 "BLOCKIRQ" }, \
+	{ BIT(APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED), "PHYS_ID_ALIASED" }, \
+	{ BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED),	 "APIC_ID_MOD" }, \
+	{ BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED),	 "APIC_BASE_MOD" }, \
+	{ BIT(APICV_INHIBIT_REASON_NESTED),		 "NESTED" }, \
+	{ BIT(APICV_INHIBIT_REASON_IRQWIN),		 "IRQWIN" }, \
+	{ BIT(APICV_INHIBIT_REASON_PIT_REINJ),		 "PIT_REINJ" }, \
+	{ BIT(APICV_INHIBIT_REASON_SEV),		 "SEV" }, \
+	{ BIT(APICV_INHIBIT_REASON_LOGICAL_ID_ALIASED),	 "LOG_ID_ALIASED" } \
+
+#define show_inhibit_reasons(inhibits) \
+	__print_flags(inhibits, "|", APICV_INHIBIT_FLAGS)
+
 TRACE_EVENT(kvm_apicv_inhibit_changed,
 	    TP_PROTO(int reason, bool set, unsigned long inhibits),
 	    TP_ARGS(reason, set, inhibits),
@@ -1388,9 +1409,12 @@ TRACE_EVENT(kvm_apicv_inhibit_changed,
 		__entry->inhibits = inhibits;
 	),
 
-	TP_printk("%s reason=%u, inhibits=0x%lx",
+	TP_printk("%s reason=%u, inhibits=0x%lx%s%s",
 		  __entry->set ? "set" : "cleared",
-		  __entry->reason, __entry->inhibits)
+		  __entry->reason, __entry->inhibits,
+		  __entry->inhibits ? " " : "",
+		  __entry->inhibits ?
+		  show_inhibit_reasons(__entry->inhibits) : "")
 );
 
 TRACE_EVENT(kvm_apicv_accept_irq,

base-commit: 7455665a3521aa7b56245c0a2810f748adc5fdd4
-- 
2.39.3