[PATCH 3.16.y-ckt 070/165] KVM: MIPS: Fix trace event to save PC directly

Luis Henriques luis.henriques at canonical.com
Wed Mar 25 14:00:43 UTC 2015

3.16.7-ckt9 -stable review patch.  If anyone has any objections, please let me know.


From: James Hogan <james.hogan at imgtec.com>

commit b3cffac04eca9af46e1e23560a8ee22b1bd36d43 upstream.

Currently the guest exit trace event saves the VCPU pointer to the
structure, and the guest PC is retrieved by dereferencing it when the
event is printed rather than directly from the trace record. This isn't
safe as the printing may occur long afterwards, after the PC has changed
and potentially after the VCPU has been freed. Usually this results in
the same (wrong) PC being printed for multiple trace events. It also
isn't portable as userland has no way to access the VCPU data structure
when interpreting the trace record itself.

Lets save the actual PC in the structure so that the correct value is
accessible later.

Fixes: 669e846e6c4e ("KVM/MIPS32: MIPS arch specific APIs for KVM")
Signed-off-by: James Hogan <james.hogan at imgtec.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Ralf Baechle <ralf at linux-mips.org>
Cc: Marcelo Tosatti <mtosatti at redhat.com>
Cc: Gleb Natapov <gleb at kernel.org>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: linux-mips at linux-mips.org
Cc: kvm at vger.kernel.org
Acked-by: Steven Rostedt <rostedt at goodmis.org>
Signed-off-by: Marcelo Tosatti <mtosatti at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 arch/mips/kvm/trace.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kvm/trace.h b/arch/mips/kvm/trace.h
index bc9e0f406c08..e51621e36152 100644
--- a/arch/mips/kvm/trace.h
+++ b/arch/mips/kvm/trace.h
@@ -26,18 +26,18 @@ TRACE_EVENT(kvm_exit,
 	    TP_PROTO(struct kvm_vcpu *vcpu, unsigned int reason),
 	    TP_ARGS(vcpu, reason),
-			__field(struct kvm_vcpu *, vcpu)
+			__field(unsigned long, pc)
 			__field(unsigned int, reason)
-			__entry->vcpu = vcpu;
+			__entry->pc = vcpu->arch.pc;
 			__entry->reason = reason;
 	    TP_printk("[%s]PC: 0x%08lx",
-		      __entry->vcpu->arch.pc)
+		      __entry->pc)
 #endif /* _TRACE_KVM_H */

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