xen/oprofile: use NMI continuation for sending virq to guest

Instead of calling send_guest_vcpu_virq() from NMI context use the
NMI continuation framework for that purpose. This avoids taking locks
in NMI mode.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/oprofile/nmi_int.c

@@ -38,6 +38,8 @@ static unsigned long saved_lvtpc[NR_CPUS];
 
 static char *cpu_type;
 
+static DEFINE_PER_CPU(struct vcpu *, nmi_cont_vcpu);
+
 static int passive_domain_msr_op_checks(unsigned int msr, int *typep, int *indexp)
 {
 	struct vpmu_struct *vpmu = vcpu_vpmu(current);
@@ -83,14 +85,27 @@ void passive_domain_destroy(struct vcpu *v)
 		model->free_msr(v);
 }
 
+bool nmi_oprofile_send_virq(void)
+{
+	struct vcpu *v = xchg(&this_cpu(nmi_cont_vcpu), NULL);
+
+	if (v)
+		send_guest_vcpu_virq(v, VIRQ_XENOPROF);
+
+	return v;
+}
+
 static int nmi_callback(const struct cpu_user_regs *regs, int cpu)
 {
 	int xen_mode, ovf;
 
 	ovf = model->check_ctrs(cpu, &cpu_msrs[cpu], regs);
 	xen_mode = ring_0(regs);
-	if ( ovf && is_active(current->domain) && !xen_mode )
-		send_guest_vcpu_virq(current, VIRQ_XENOPROF);
+	if (ovf && is_active(current->domain) && !xen_mode &&
+	    !this_cpu(nmi_cont_vcpu)) {
+		this_cpu(nmi_cont_vcpu) = current;
+		trigger_nmi_continuation();
+	}
 
 	if ( ovf == 2 )
 		current->arch.nmi_pending = true;

xen/arch/x86/traps.c

@@ -65,6 +65,7 @@
 #include <asm/debugger.h>
 #include <asm/msr.h>
 #include <asm/nmi.h>
+#include <asm/xenoprof.h>
 #include <asm/shared.h>
 #include <asm/x86_emulate.h>
 #include <asm/traps.h>
@@ -1805,6 +1806,9 @@ bool nmi_check_continuation(void)
 {
     bool ret = false;
 
+    if ( nmi_oprofile_send_virq() )
+        ret = true;
+
     return ret;
 }
 

xen/include/asm-x86/xenoprof.h

@@ -69,6 +69,8 @@ int passive_domain_do_rdmsr(unsigned int msr, uint64_t *msr_content);
 int passive_domain_do_wrmsr(unsigned int msr, uint64_t msr_content);
 void passive_domain_destroy(struct vcpu *v);
 
+bool nmi_oprofile_send_virq(void);
+
 #else
 
 static inline int passive_domain_do_rdmsr(unsigned int msr,
@@ -85,6 +87,11 @@ static inline int passive_domain_do_wrmsr(unsigned int msr,
 
 static inline void passive_domain_destroy(struct vcpu *v) {}
 
+static inline bool nmi_oprofile_send_virq(void)
+{
+    return false;
+}
+
 #endif /* CONFIG_XENOPROF */
 
 #endif /* __ASM_X86_XENOPROF_H__ */