linux-kernel - Re: [PATCH v3 4/4] x86/cpu/topology: Check for X86_FEATURE_XTOPOLOGY instead of passing has

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87jz2s3h2b.ffs@tglx>
Date: Sun, 24 Aug 2025 16:55:24 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: K Prateek Nayak <kprateek.nayak@....com>, Ingo Molnar
 <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org
Cc: Naveen rao <naveen.rao@....com>, Sairaj Kodilkar <sarunkod@....com>, "H.
 Peter Anvin" <hpa@...or.com>, "Peter Zijlstra (Intel)"
 <peterz@...radead.org>, "Xin Li (Intel)" <xin@...or.com>, Pawan Gupta
 <pawan.kumar.gupta@...ux.intel.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org, Mario Limonciello <mario.limonciello@....com>,
 "Gautham R. Shenoy" <gautham.shenoy@....com>, Babu Moger
 <babu.moger@....com>, Suravee Suthikulpanit
 <suravee.suthikulpanit@....com>, K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [PATCH v3 4/4] x86/cpu/topology: Check for
 X86_FEATURE_XTOPOLOGY instead of passing has_topoext

On Sun, Aug 24 2025 at 15:38, Thomas Gleixner wrote:
>> -	if (!has_topoext) {
>> +	if (!cpu_feature_enabled(X86_FEATURE_XTOPOLOGY)) {
>>  		/*
>>  		 * Prefer initial_apicid parsed from XTOPOLOGY leaf
>>  		 * 0x8000026 or 0xb if available. Otherwise prefer the
>
> That's patently wrong.
>
> The leaves might be "available", but are not guaranteed to be valid. So
> FEATURE_XTOPOLOGY gives you the wrong answer.
>
> The has_topoext logic is there for a reason.

Hrm. I have to correct myself. It's set by the 0xb... parsing when that
finds a valid leaf. My memory tricked me on that.

So yes, it can be used for that, but that's a cleanup. The simple fix
should be applied first as that's trivial to backport.