linux-kernel - Re: [PATCH linux v3 2/9] x86/acpi: store ACPI ids from MADT for future usage

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Date:   Wed, 1 Mar 2017 20:54:44 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, Stefano Stabellini <sstabellini@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Vrabel <david.vrabel@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Jan Beulich <JBeulich@...e.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Julien Grall <julien.grall@....com>
Subject: Re: [PATCH linux v3 2/9] x86/acpi: store ACPI ids from MADT for
 future usage

On Tue, 26 Jul 2016, Vitaly Kuznetsov wrote:

So this patch made it's way into Linus tree via XEN w/o an ack or reviewed
by from the x86 maintainers.

Yes, we were on CC, but it's not that hard to ping the maintainers when
they do not respond on a particular patch.

The whole series ran under the cover letter subject:

 xen: pvhvm: support bootup on secondary vCPU

which suggests that this is a XEN internal affair. And I really have enough
stuff to look after so I don't dive into XEN internals if it's not
obviously required.

Let's look at this after the fact:

> Currently we don't save ACPI ids (unlike LAPIC ids which go to
> x86_cpu_to_apicid) from MADT and we may need this information later.

may need? Maybe, or maybe not.

> Particularly, ACPI ids is the only existent way for a PVHVM Xen guest
> to figure out Xen's idea of its vCPUs ids before these CPUs boot and
> in some cases these ids diverge from Linux's cpu ids.

I have no idea what this sentence means and what kind of divergence this is
talking about.

Dammit, if stuff gets slammed into the x86 tree w/o a proper notice, then
the minimum requirement is at least an understandable changelog which
allows non XEN experts to figure out WHY this is necessary and WHAT this is
about.

> @@ -714,7 +722,7 @@ int acpi_map_cpu(acpi_handle handle, phys_cpuid_t physid, int *pcpu)
>  {
>  	int cpu;
>  
> -	cpu = acpi_register_lapic(physid, ACPI_MADT_ENABLED);
> +	cpu = acpi_register_lapic(physid, U32_MAX, ACPI_MADT_ENABLED);

What the heck is this? ACPIID is U32_MAX? Sure, that's obvious as it can
get and the well thought out comment above this call explains it nicely.

Yes, I know it has been fixed later, but this crap should not have been
merged in the first place.

Yours grumpy

      tglx