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Subject: Re: [PATCH v4 2/2] xen: delay xen_hvm_init_time_ops() if kdump is
 boot on vcpu>=32
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        xen-devel@lists.xenproject.org, x86@kernel.org
Cc:     linux-kernel@vger.kernel.org, jgross@suse.com,
        sstabellini@kernel.org, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, dave.hansen@linux.intel.com, joe.jin@oracle.com
References: <20220302164032.14569-1-dongli.zhang@oracle.com>
 <20220302164032.14569-3-dongli.zhang@oracle.com>
 <bacae45c-9f8e-456b-1036-7f68e1e4374d@oracle.com>
From:   Dongli Zhang <dongli.zhang@oracle.com>
Message-ID: <0ac50fb6-0aca-e61a-1f38-8badbc8c967a@oracle.com>
Date:   Wed, 2 Mar 2022 16:31:51 -0800
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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".

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
>>