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Re: [PATCH v4 2/2] xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32
- To: Dongli Zhang <dongli.zhang@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, x86@xxxxxxxxxx
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Wed, 2 Mar 2022 21:11:24 -0500
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- Delivery-date: Thu, 03 Mar 2022 02:11:58 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 3/2/22 7:31 PM, Dongli Zhang wrote:
Hi Boris,
On 3/2/22 4:20 PM, Boris Ostrovsky wrote:
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?
I just want to keep above sync with ....
-boris
if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {
pr_info("Xen doesn't support pvclock on HVM, disable pv timer");
+ goto exit;
+ }
... here.
That is, I want the main logic of xen_hvm_init_time_ops() to run for at most
once. Both of above two if statements will "go to exit".
I didn't notice this actually.
I think both of them should return early, there is no reason to set
hvm_time_initialized to true when, in fact, we have not initialized anything.
And to avoid printing the warning twice we can just replace it with
pr_info_once().
I can fix it up when committing so no need to resend. So unless you disagree
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Thank you very much!
Dongli Zhang
+
+ /*
+ * 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
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