Re: [Xen-devel] [PATCH v7 09/10] microcode: remove microcode_update_lock

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.06.19 at 14:46, <chao.gao@xxxxxxxxx> wrote:
> On Wed, Jun 05, 2019 at 08:53:46AM -0600, Jan Beulich wrote:
>>>>> On 27.05.19 at 10:31, <chao.gao@xxxxxxxxx> wrote:
>>> @@ -307,8 +303,7 @@ static int apply_microcode(const struct microcode_patch 
>>> *patch)
>>>  
>>>      mc_intel = patch->mc_intel;
>>>  
>>> -    /* serialize access to the physical write to MSR 0x79 */
>>> -    spin_lock_irqsave(&microcode_update_lock, flags);
>>> +    BUG_ON(local_irq_is_enabled());
>>>  
>>>      /*
>>>       * Writeback and invalidate caches before updating microcode to avoid
>>
>>Thinking about it - what happens if we hit an NMI or #MC here?
>>watchdog_disable(), a call to which you add in an earlier patch,
>>doesn't really suppress the generation of NMIs, it only tells the
>>handler not to look at the accumulated statistics.
> 
> I think they should be suppressed. Ashok, could you confirm it?
> 
> I will figure out how to suppress them in Xen.

Well, afaik suppressing #MC is impossible. CR4.MCE clear leads
to immediate shutdown in case of a machine check, unless I'm
mistaken. The watchdog NMI, otoh, could of course be "properly"
disabled.

Jan



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