Re: [PATCH v4 2/2] xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32

[Boris Ostrovsky]

On 3/2/22 11:40 AM, Dongli Zhang wrote:

  void __init xen_hvm_init_time_ops(void)
  {
+       static bool hvm_time_initialized;
+
+       if (hvm_time_initialized)
+               return;
+
        /*
         * vector callback is needed otherwise we cannot receive interrupts
         * on cpu > 0 and at this point we don't know how many cpus are
         * available.
         */
        if (!xen_have_vector_callback)
-               return;
+               goto exit;

Why not just return? Do we expect the value of xen_have_vector_callback to 
change?


-boris

if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {

                pr_info("Xen doesn't support pvclock on HVM, disable pv timer");
+               goto exit;
+       }
+
+       /*
+        * Only MAX_VIRT_CPUS 'vcpu_info' are embedded inside 'shared_info'.
+        * The __this_cpu_read(xen_vcpu) is still NULL when Xen HVM guest
+        * boots on vcpu >= MAX_VIRT_CPUS (e.g., kexec), To access
+        * __this_cpu_read(xen_vcpu) via xen_clocksource_read() will panic.
+        *
+        * The xen_hvm_init_time_ops() should be called again later after
+        * __this_cpu_read(xen_vcpu) is available.
+        */
+       if (!__this_cpu_read(xen_vcpu)) {
+               pr_info("Delay xen_init_time_common() as kernel is running on 
vcpu=%d\n",
+                       xen_vcpu_nr(0));
                return;
        }

@@ -577,6 +597,9 @@ void __init xen_hvm_init_time_ops(void)

        x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;

x86_platform.set_wallclock = xen_set_wallclock;

+
+exit:
+       hvm_time_initialized = true;
  }
  #endif