[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <36462e78-8014-4415-bc47-86fbb46d028b@citrix.com>
Date: Fri, 3 Nov 2023 19:58:01 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, Steve Wahl <steve.wahl@....com>,
Justin Ernst <justin.ernst@....com>,
Kyle Meyer <kyle.meyer@....com>,
Dimitri Sivanich <dimitri.sivanich@....com>,
Russ Anderson <russ.anderson@....com>,
Darren Hart <dvhart@...radead.org>,
Andy Shevchenko <andy@...radead.org>,
"K. Y. Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Krzysztof Wilczyński <kw@...ux.com>,
Rob Herring <robh@...nel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Notes on BAD_APICID, Was: [PATCH 0/3] x86/apic: Misc pruning
On 02/11/2023 12:26 pm, Andrew Cooper wrote:
> Seriously, this work started out trying to fix a buggy comment. It
> escalated somewhat... Perform some simple tidying.
Another dodgy construct spotted while doing this work is
#ifdef CONFIG_X86_32
#define BAD_APICID 0xFFu
#else
#define BAD_APICID 0xFFFFu
#endif
considering that both of those "bad" values are legal APIC IDs in an
x2APIC system.
The majority use is as a sentential (of varying types - int, u16
mostly), although the uses for NUM_APIC_CLUSTERS, and
safe_smp_processor_id() look suspect.
In particular, safe_smp_processor_id() *will* malfunction on some legal
CPUs, and needs to use -1 (32 bits wide) to spot the intended error case
of a bad xAPIC mapping.
However, it's use in amd_pmu_cpu_starting() from topology_die_id() looks
broken. Partly because the error handling is (only) a WARN_ON_ONCE(),
and also because nb->nb_id's sentinel value is -1 of type int.
I suspect there's a lot of cleaning to be done here too.
~Andrew
Powered by blists - more mailing lists