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Date: Mon, 11 May 2009 13:06:16 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Yinghai Lu <yinghai@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
       "H. Peter Anvin" <hpa@zytor.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Ed Swierk <eswierk@aristanetworks.com>
Subject: Re: [PATCH] x86: read apic id if it is not acpi_lapic -v2
Message-ID: <20090511110616.GI4648@elte.hu>
References: <20090430084145.GD21699@elte.hu> <49FBD0A2.4030309@kernel.org> <20090502070254.GA4791@lenovo> <49FC85A9.2070702@kernel.org> <20090511092655.GC26444@elte.hu> <20090511094056.GB4624@lenovo>
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* Cyrill Gorcunov <gorcunov@gmail.com> wrote:

> [Ingo Molnar - Mon, May 11, 2009 at 11:26:55AM +0200]
> | 
> | * Yinghai Lu <yinghai@kernel.org> wrote:
> | 
> | > @@ -1590,21 +1591,32 @@ void __init init_apic_mappings(void)
> | >  	} else
> | >  		apic_phys = mp_lapic_addr;
> | >  
> | > -	set_fixmap_nocache(FIX_APIC_BASE, apic_phys);
> | > +	/* lets check if we may to NOP'ify apic operations */
> | > +	if (!cpu_has_apic) {
> | > +		pr_info("APIC: disable apic facility\n");
> | > +		apic_disable();
> | > +		return;
> | > +	}
> | > +
> | > +	/*
> | > +	 * acpi lapic path already map that address in
> | > +	 * acpi_register_lapic_address()
> | > +	 */
> | >  	apic_printk(APIC_VERBOSE, "mapped APIC to %08lx (%08lx)\n",
> | >  				APIC_BASE, apic_phys);
> | > +	if (acpi_lapic)
> | > +		return;
> | 
> | why do we return here? We should sanity-check the APIC ID even if we 
> | come from ACPI.
> | 
> | 	Ingo
> | 
> 
> I believe we already have it checked in 
> acpi_register_lapic_address so no need to do it twice. Or I miss 
> something?

It's better to have such checks applied redundantly instead of 
introducing such implicit criss-cross dependencies between 
functions. (which would break if acpi_register_lapic_address() ever 
stopped checking the apic id - or did it differently)

	Ingo