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Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with platform legacy quirk

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On 08/04/16 08:56, Luis R. Rodriguez wrote:
> On Thu, Apr 7, 2016 at 11:38 PM, Juergen Gross <jgross@suse.com> wrote:
>> On 08/04/16 08:29, Luis R. Rodriguez wrote:
>>> On Thu, Apr 7, 2016 at 10:18 PM, Juergen Gross <jgross@suse.com> wrote:
>>>> On 08/04/16 02:32, Luis R. Rodriguez wrote:
>>>>> This highlights a semantic gap issue. From a quick cursory review, I think
>>>>> we can address this temporarily by just using a check:
>>>>>
>>>>> void __init x86_early_init_platform_quirks(void)
>>>>> {
>>>>>       x86_platform.legacy.rtc = 1;
>>>>>
>>>>>       switch (boot_params.hdr.hardware_subarch) {
>>>>>       case X86_SUBARCH_XEN:
>>>>>       case X86_SUBARCH_LGUEST:
>>>>>       case X86_SUBARCH_INTEL_MID:
>>>>> -             x86_platform.legacy.rtc = 0;
>>>>> +             if (x86_init.mpparse.get_smp_config != x86_init_uint_noop)
>>>>> +                     x86_platform.legacy.rtc = 0;
>>>>
>>>> No! Why don't you just use the explicit test xen_initial_domain() ?
>>>
>>> Because we don't want to sprinkle Xen specific code outside of Xen
>>> code. What do you think about the second possibility I listed?
>>> Otherwise, any other ideas?
>>
>> Don't try to guess.
> 
> I can only do that given there is nothing at all to tell me what to
> expect here with regards to RTC on Xen guest, if there is some
> documentation that could help with that please let me know.

Only Xen inernals. :-)

> 
>> In case you don't want to inject Xen internals here, just call a Xen
>> function to either return the correct value, or to set all structure
>> elements correctly.
> 
> I like the later as an option, in case there are further hardware
> subarch specific quirks which require internal logistics. What do
> others think?
> 
>> Thinking more about it: why not do that for all the subarchs?
> 
> I originally had went with that approach, but Ingo made the point that
> it would be best to instead move all quirk settings into one place.
> That lets a reader easily tell what is going on in one place, it also
> compartmentalizes the hardware subarch uses.

Okay. Another idea (not sure whether this is really a good one):

Add X86_SUBARCH_XEN_DOM0. As hardware_subarch is 32 bits wide I don't
think the number of subarchs is a scarce resource. :-)

I'd expect other quirks in future might have different settings for
domU and dom0, too.

>> You'd
>> have the specific settings where they belong: in a subarch specific
>> source. Just do the default settings in x86_early_init_platform_quirks()
>> and let the subarch functions set the non-default values.
> 
> This is a rather different approach than what I had originally tried.
> Bike shed thing -- someone just has to decide.
> 
> Left up to me, I kind of really like centralizing the quirk settings
> in one place approach as it means a reader can easily tell what's
> going on regardless of platform in one place for odd settings. I
> prefer this given that we *already* have the semantics over hardware
> subarch in a generalized fashion. We *do not* have semantics for dom0
> Vs domU -- if such a notion is generic to other virtualization

That's not carved in stone - see above. :-)

> environments it deserves consideration to new semantics to deal with
> that, otherwise the callback for handling further quirks is best, but
> I'd also highly discourage such callback to be used.


Juergen

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[PATCH v4 00/14] x86: remove paravirt_enabled "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 06/14] x86/init: use a platform legacy quirk for ebda "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [Xen-devel] [PATCH v4 06/14] x86/init: use a platform legacy  quirk for ebda David Vrabel <david.vrabel@citrix.com> - 2016-04-07 11:50 +0200
      Re: [Xen-devel] [PATCH v4 06/14] x86/init: use a platform legacy  quirk for ebda "Luis R. Rodriguez" <mcgrof@suse.com> - 2016-04-07 23:10 +0200
  [PATCH v4 10/14] x86/cpu/intel: remove not needed paravirt_enabled() for f00f work around "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 14/14] x86/paravirt: remove paravirt_enabled() "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 13/14] x86/init: rename ebda code file "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [Xen-devel] [PATCH v4 04/14] x86/rtc: replace paravirt rtc check  with platform legacy quirk David Vrabel <david.vrabel@citrix.com> - 2016-04-07 11:50 +0200
      Re: [Xen-devel] [PATCH v4 04/14] x86/rtc: replace paravirt rtc check  with platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-14 01:10 +0200
    Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-07 15:00 +0200
      Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 02:40 +0200
        Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 07:20 +0200
          Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 08:40 +0200
            Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 09:00 +0200
              Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 09:20 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 09:40 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Juergen Gross <jgross@suse.com> - 2016-04-08 10:10 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-08 14:40 +0200
                Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 20:50 +0200
          Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 08:40 +0200
            Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with  platform legacy quirk Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-08 14:30 +0200
  [PATCH v4 07/14] tools/lguest: force disable tboot and apm "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [PATCH v4 07/14] tools/lguest: force disable tboot and apm Rusty Russell <rusty@rustcorp.com.au> - 2016-04-11 06:00 +0200
  [PATCH v4 03/14] tools/lguest: make lguest launcher use X86_SUBARCH_LGUEST explicitly "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 08/14] apm32: remove paravirt_enabled() use "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [PATCH v4 08/14] apm32: remove paravirt_enabled() use Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-04-07 15:10 +0200
      Re: [PATCH v4 08/14] apm32: remove paravirt_enabled() use "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 00:40 +0200
  [PATCH v4 12/14] x86, ACPI: parse ACPI_FADT_LEGACY_DEVICES "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 01/14] x86/boot: enumerate documentation for the x86 hardware_subarch "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
    Re: [PATCH v4 01/14] x86/boot: enumerate documentation for the x86  hardware_subarch Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2016-04-07 13:30 +0200
      Re: [PATCH v4 01/14] x86/boot: enumerate documentation for the x86  hardware_subarch "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 00:40 +0200
  [PATCH v4 09/14] x86/tboot: remove paravirt_enabled() "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:10 +0200
  [PATCH v4 02/14] x86/xen: use X86_SUBARCH_XEN for PV guest boots "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:20 +0200
    Re: [Xen-devel] [PATCH v4 02/14] x86/xen: use X86_SUBARCH_XEN for PV  guest boots David Vrabel <david.vrabel@citrix.com> - 2016-04-07 11:50 +0200
  [PATCH v4 05/14] x86, ACPI: move ACPI_FADT_NO_CMOS_RTC check to ACPI boot code "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 02:20 +0200
  Re: [Xen-devel] [PATCH v4 00/14] x86: remove paravirt_enabled Juergen Gross <jgross@suse.com> - 2016-04-07 15:30 +0200
  [PATCH v4 13/14] x86/init: rename ebda code file "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-07 23:40 +0200
  Re: [PATCH v4 00/14] x86: remove paravirt_enabled "Luis R. Rodriguez" <mcgrof@kernel.org> - 2016-04-08 03:20 +0200
    Re: [PATCH v4 00/14] x86: remove paravirt_enabled Borislav Petkov <bp@alien8.de> - 2016-04-08 12:30 +0200

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