linux-kernel - Re: [PATCH] x86/cpufeatures: Correct LKGS feature flag description

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Message-ID: <4CDD31CE-7040-4ADB-B3F1-E095E3C5BDF5@zytor.com>
Date: Wed, 15 Oct 2025 20:12:08 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Borislav Petkov <bp@...en8.de>
CC: Xin Li <xin@...or.com>, Borislav Petkov <bp@...nel.org>,
        Xin Li <xin3.li@...el.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/cpufeatures: Correct LKGS feature flag description

On October 15, 2025 8:49:11 AM PDT, Borislav Petkov <bp@...en8.de> wrote:
>On Wed, Oct 15, 2025 at 08:44:55AM -0700, H. Peter Anvin wrote:
>> >> Except that that is also wrong, because that's not all of what the instruction does. "Load user space GS" is really what it does, despite the initiate historical naming.
>> >> 
>> >
>> >Do you mean the load of GS attributes by LKGS is still missing?
>> 
>> Yes. It's really a modified MOV GS,... instruction that loads the base, limit, selector, and attributes; it just loads the base into a different place.
>
>Ok, "Load user space GS base" it is. Considering how you can't load any other
>GS.base due to it GPing for CPL > 0.
>

No, "load user space GS." It loads everything, not just the base.