linux-kernel - [PATCH 6/6] KVM: x86: Add requested index to the CPUID tracepoint

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Date:   Mon,  2 Mar 2020 11:57:36 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jan Kiszka <jan.kiszka@...mens.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [PATCH 6/6] KVM: x86: Add requested index to the CPUID tracepoint

Output the requested index when tracing CPUID emulation; it's basically
mandatory for leafs where the index is meaningful, and is helpful for
verifying KVM correctness even when the index isn't meaningful, e.g. the
trace for a Linux guest's hypervisor_cpuid_base() probing appears to
be broken (returns all zeroes) at first glance, but is correct because
the index is non-zero, i.e. the output values correspond to random index
in the maximum basic leaf.

Suggested-by: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: Jan Kiszka <jan.kiszka@...mens.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/cpuid.c |  3 ++-
 arch/x86/kvm/trace.h | 13 ++++++++-----
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b0a4f3c17932..a3c9f6bf43f3 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1047,7 +1047,8 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 			}
 		}
 	}
-	trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, exact_entry_exists);
+	trace_kvm_cpuid(function, index, *eax, *ebx, *ecx, *edx,
+			exact_entry_exists);
 }
 EXPORT_SYMBOL_GPL(kvm_cpuid);
 
diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index f194dd058470..aa372d0119f0 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -151,12 +151,14 @@ TRACE_EVENT(kvm_fast_mmio,
  * Tracepoint for cpuid.
  */
 TRACE_EVENT(kvm_cpuid,
-	TP_PROTO(unsigned int function, unsigned long rax, unsigned long rbx,
-		 unsigned long rcx, unsigned long rdx, bool found),
-	TP_ARGS(function, rax, rbx, rcx, rdx, found),
+	TP_PROTO(unsigned int function, unsigned int index, unsigned long rax,
+		 unsigned long rbx, unsigned long rcx, unsigned long rdx,
+		 bool found),
+	TP_ARGS(function, index, rax, rbx, rcx, rdx, found),
 
 	TP_STRUCT__entry(
 		__field(	unsigned int,	function	)
+		__field(	unsigned int,	index		)
 		__field(	unsigned long,	rax		)
 		__field(	unsigned long,	rbx		)
 		__field(	unsigned long,	rcx		)
@@ -166,6 +168,7 @@ TRACE_EVENT(kvm_cpuid,
 
 	TP_fast_assign(
 		__entry->function	= function;
+		__entry->index		= index;
 		__entry->rax		= rax;
 		__entry->rbx		= rbx;
 		__entry->rcx		= rcx;
@@ -173,8 +176,8 @@ TRACE_EVENT(kvm_cpuid,
 		__entry->found		= found;
 	),
 
-	TP_printk("func %x rax %lx rbx %lx rcx %lx rdx %lx, cpuid entry %s",
-		  __entry->function, __entry->rax,
+	TP_printk("func %x idx %x rax %lx rbx %lx rcx %lx rdx %lx, cpuid entry %s",
+		  __entry->function, __entry->index, __entry->rax,
 		  __entry->rbx, __entry->rcx, __entry->rdx,
 		  __entry->found ? "found" : "not found")
 );
-- 
2.24.1