linux-kernel - Re: [PATCH] x86/cpufeatures: Free up unused feature bits

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Message-ID: <2708a7af-e4b5-4268-87dc-042d8472f635@intel.com>
Date: Fri, 8 Nov 2024 10:46:23 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Sohil Mehta <sohil.mehta@...el.com>, "H. Peter Anvin" <hpa@...or.com>,
 x86@...nel.org, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Sean Christopherson <seanjc@...gle.com>, Tony Luck <tony.luck@...el.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/cpufeatures: Free up unused feature bits

On 11/8/24 10:42, Sohil Mehta wrote:
>> udev might try to load the old module on a new CPU with
>> X86_FEATURE_WHIZZY_NEW_FEATURE that's not a P3.
>>
> So an old coretemp module could get loaded when the above TDX bit is
> set. Not sure how likely this scenario is or what can we do to avoid it now?

Pretty unlikely that someone would change the bit, have modversions
disabled, *AND* need to load a module built before the bit changed.

I think we can mostly ignore it.  If we break something, it _can_ be
backed out and fixed.