Messages in this thread | | | Date | Tue, 29 Jan 2013 08:47:46 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/apic: check FADT settings after enable x2apic |
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* Yinghai Lu <yinghai@kernel.org> wrote:
> On Mon, Jan 28, 2013 at 2:11 AM, Ingo Molnar <mingo@kernel.org> wrote: > > > >> HP has systems that work with x2apic phys mode and BIOS set > >> ACPI_FADT_APIC_PHYSICAL in FADT table, and all cpuid < 255, > >> the spec requires BIOS only put system on xapic mode. Kernel > > > > Which spec? > > > >> will set to x2apic logical mode instead of x2apic phys mode. > > > > Which has exactly what bad effect on users of these systems? > > > > You left out the most important information from the changelog: > > why do users care, what good does the patch do? > > please check you are happy with this: > > --- > From: Stoney Wang <song-bo.wang@hp.com> > Subject: [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys_probe() > > HP has systems that only work with x2apic phys mode and BIOS set > ACPI_FADT_APIC_PHYSICAL in FADT table. But all apicid < 255, > according to x2apic-spec, chapter 2.9, BIOS need to pass the control > to the OS with xapic mode. > Kernel will set apic driver wrong to x2apic cluster instead of x2apic phys. > > The user will have to append nox2apic in boot command line to stay xapic mode, > or append x2apic_phys to switch to x2apic phys mode.
This still does not explain what happens if none of this user action is taken. I.e. what exact _user visible problem_ does the patch fix?
Is this really so unimportant to you? Almost everyone will start a changelog with explaining what badness happens. Not you - you explain everything from how the fix works to how to work around the bug - except describing the most important thing: theuser visible problem itself ... Weird.
Thanks,
Ingo
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