Re: [PATCH 3/7] x86/boot: Collect the Raw CPU Policy earlier on boot

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/05/2024 4:44 pm, Jan Beulich wrote:
> On 23.05.2024 13:16, Andrew Cooper wrote:
>> This is a tangle, but it's a small step in the right direction.
>>
>> xstate_init() is shortly going to want data from the Raw policy.
>> calculate_raw_cpu_policy() is sufficiently separate from the other policies 
>> to
>> be safe to do.
>>
>> No functional change.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Would you mind taking a look at
> https://lists.xen.org/archives/html/xen-devel/2021-04/msg01335.html
> to make clear (to me at least) in how far we can perhaps find common grounds
> on what wants doing when? (Of course the local version I have has been
> constantly re-based, so some of the function names would have changed from
> what's visible there.)

That's been covered several times, at least in part.

I want to eventually move the host policy too, but I'm not willing to
compound the mess we've currently got just to do it earlier.  It's just
creating even more obstacles to doing it nicely.

Nothing in this series needs (or indeed should) use the host policy.

The same is true of your AMX series.  You're (correctly) breaking the
uniform allocation size and (when policy selection is ordered WRT vCPU
creation, as discussed) it becomes solely depend on the guest policy.

xsave.c really has no legitimate use for the host policy once the
uniform allocation size aspect has gone away.


>> --- a/xen/arch/x86/cpu-policy.c
>> +++ b/xen/arch/x86/cpu-policy.c
>> @@ -845,7 +845,6 @@ static void __init calculate_hvm_def_policy(void)
>>  
>>  void __init init_guest_cpu_policies(void)
>>  {
>> -    calculate_raw_cpu_policy();
>>      calculate_host_policy();
>>  
>>      if ( IS_ENABLED(CONFIG_PV) )
>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -1888,7 +1888,9 @@ void asmlinkage __init noreturn __start_xen(unsigned 
>> long mbi_p)
>>  
>>      tsx_init(); /* Needs microcode.  May change HLE/RTM feature bits. */
>>  
>> -    identify_cpu(&boot_cpu_data);
>> +    calculate_raw_cpu_policy(); /* Needs microcode.  No other dependenices. 
>> */
>> +
>> +    identify_cpu(&boot_cpu_data); /* Needs microcode and raw policy. */
> You don't introduce any dependency on raw policy here, and there cannot 
> possibly
> have been such a dependency before (unless there was a bug somewhere). 
> Therefore
> I consider this latter comment misleading at this point.

It's made true by the next patch, and I'm not included to split the
comment across two patches which are going to be committed together in a
unit.

~Andrew