[Xen-devel] [PATCH] x86/vpmu: add cpu hot unplug notifier for vpmu

[Luwei Kang <luwei.kang@xxxxxxxxx>]

Currently, hot unplug a cpu with vpmu enabled may cause system
hang due to send IPI to a die physical cpu. This patch add a
cpu hot unplug notifer to save vpmu context before cpu offline.

Consider one scene, hotplug physical cpu N with vpmu is enabled.
The vcpu which running on this physical cpu before will be switch
to other online cpu. Before load the vpmu context to new physical
cpu, a IPI will be send to cpu N to save the vpmu context.
System will hang in function on_select_cpus because of that
physical cpu is offline and can not do any response.

Signed-off-by: Luwei Kang <luwei.kang@xxxxxxxxx>
---
 xen/arch/x86/cpu/vpmu.c | 36 ++++++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/cpu/vpmu.c b/xen/arch/x86/cpu/vpmu.c
index 03401fd..89e0ea8 100644
--- a/xen/arch/x86/cpu/vpmu.c
+++ b/xen/arch/x86/cpu/vpmu.c
@@ -35,6 +35,7 @@
 #include <asm/apic.h>
 #include <public/pmu.h>
 #include <xsm/xsm.h>
+#include <xen/cpu.h>
 
 #include <compat/pmu.h>
 CHECK_pmu_cntr_pair;
@@ -835,6 +836,36 @@ long do_xenpmu_op(unsigned int op, 
XEN_GUEST_HANDLE_PARAM(xen_pmu_params_t) arg)
     return ret;
 }
 
+static int cpu_callback(struct notifier_block *nfb, unsigned long action, void 
*hcpu)
+{
+    unsigned int cpu = (unsigned long)hcpu;
+    struct vcpu *vcpu = per_cpu(last_vcpu, cpu);
+    struct vpmu_struct *vpmu;
+
+    if ( !vcpu )
+        return NOTIFY_DONE;
+
+    vpmu = vcpu_vpmu(vcpu);
+    if ( !vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) )
+        return NOTIFY_DONE;
+
+    switch ( action )
+    {
+    case CPU_DYING:
+        vpmu_save_force(vcpu);
+        vpmu_reset(vpmu, VPMU_CONTEXT_LOADED);
+        break;
+    default:
+        break;
+    }
+
+    return NOTIFY_DONE;
+}
+
+static struct notifier_block vpmu_cpu_nfb = {
+    .notifier_call = cpu_callback
+};
+
 static int __init vpmu_init(void)
 {
     int vendor = current_cpu_data.x86_vendor;
@@ -871,10 +902,11 @@ static int __init vpmu_init(void)
         break;
     }
 
-    if ( vpmu_mode != XENPMU_MODE_OFF )
+    if ( vpmu_mode != XENPMU_MODE_OFF ) {
+        register_cpu_notifier(&vpmu_cpu_nfb);
         printk(XENLOG_INFO "VPMU: version " __stringify(XENPMU_VER_MAJ) "."
                __stringify(XENPMU_VER_MIN) "\n");
-    else
+    } else
         opt_vpmu_enabled = 0;
 
     return 0;
-- 
1.8.3.1


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