* Yinghai Lu <ying...@kernel.org> wrote:
> On Mon, Jan 28, 2013 at 2:11 AM, Ingo Molnar <mi...@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.w...@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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