Re: [Xen-devel] [PATCH v5 7/8] x86/microcode: Synchronize late microcode loading

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Roger Pau Monné <roger.pau@xxxxxxxxxx> 01/29/19 11:39 AM >>>
>On Mon, Jan 28, 2019 at 03:06:49PM +0800, Chao Gao wrote:
>> +    /*
>> +     * Initiate an update on all processors which don't have an online 
>> sibling
>> +     * thread with a lower thread id. Other sibling threads just await the
>> +     * completion of microcode update.
>> +     */
>> +    if ( cpu == cpumask_first(per_cpu(cpu_sibling_mask, cpu)) )
>> +        ret = microcode_update_cpu();
>
>The description says "Gather all cores and serialize the microcode
>update on them by doing it one-by-one" but it looks like you are doing
>the update in parallel actually?

As discussed in the context of earlier versions, the apparent parallelism
here goes away immediately inside microcode_update_cpu(), which

acquires a global spin lock first thing.


Jan


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