Re: [Xen-devel] [PATCH] x86/XPTI: fix S3 resume (and CPU offlining in general)

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.05.18 at 15:48, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 24/05/18 14:41, Jan Beulich wrote:
>> In commit d1d6fc97d6 ("x86/xpti: really hide almost all of Xen image")
>> I've failed to remember the fact that multiple CPUs share a stub
>> mapping page. Therefore it is wrong to unconditionally zap the mapping
>> when bringing down a CPU; it may only be unmapped when no other online
>> CPU uses that same page.
>>
>> Reported-by: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> --- a/xen/arch/x86/smpboot.c
>> +++ b/xen/arch/x86/smpboot.c
>> @@ -876,7 +876,21 @@ static void cleanup_cpu_root_pgt(unsigne
>>  
>>      free_xen_pagetable(rpt);
>>  
>> -    /* Also zap the stub mapping for this CPU. */
>> +    /*
>> +     * Also zap the stub mapping for this CPU, if no other online one uses
>> +     * the same page.
>> +     */
>> +    if ( stub_linear )
>> +    {
>> +        unsigned int other;
>> +
>> +        for_each_online_cpu(other)
> 
> Look over the code, it seems that with spaces is the more common style,
> but it is admittedly fairly mixed.

I'd prefer to leave it as is - personally I don't consider "for_each_online_cpu"
and alike keywords, which is what ./CODING_STYLE talks about. I accept
others taking a different position, i.e. I don't normally demand a particular
style to be used there, but in code I write I prefer to only apply spaces to
real keywords.

> Either way (as that's trivial to fix), Acked-by: Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>

Thanks, Jan



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