linux-kernel - Re: [tip:x86/urgent] x86/apic: Fix signedness bug in APIC ID validity checks

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Date:   Wed, 11 Apr 2018 15:01:54 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     <peterz@...radead.org>, <lirongqing@...du.com>,
        <linux-kernel@...r.kernel.org>, <mingo@...nel.org>,
        <hpa@...or.com>, <tglx@...utronix.de>,
        <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/urgent] x86/apic: Fix signedness bug in APIC ID validity
 checks

Hi Thomas,

At 04/10/2018 10:51 PM, tip-bot for Li RongQing wrote:
[...]

> x86/apic: Fix signedness bug in APIC ID validity checks
> 
> The APIC ID as parsed from ACPI MADT is validity checked with the
> apic->apic_id_valid() callback, which depends on the selected APIC type.
> 
> For non X2APIC types APIC IDs >= 0xFF are invalid, but values > 0x7FFFFFFF

Today when I am reading "Intel® 64 Architecture x2APIC Specification", I
find that below in chapter 2.4.1:

   The APIC ID value of FFFF_FFFFH and the highest value corresponding to
   the imple-mented bit-width of the local APIC ID register in the system
   are reserved and cannot be assigned to any logical processor.

Seems, FFFF_FFFFH is also invalid for X2APIC types, Shall we also do the
validity check for X2APIC ID?

acpi_parse_x2apic()
	...
	/* Ignore invalid ID */
	if (apic_id == 0xffffffff)
		return 0;
	...

Thanks,
	dou