linux-kernel - Re: [PATCH v6 5/5] x86/gsseg: use the LKGS instruction if available for load_gs

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Message-ID: <2B27D0A2-B1D0-4347-8587-DCFDB05BF683@zytor.com>
Date: Mon, 01 Jul 2024 01:01:54 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Borislav Petkov <bp@...en8.de>
CC: Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org, x86@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        peterz@...radead.org, brgerst@...il.com, chang.seok.bae@...el.com,
        jgross@...e.com
Subject: Re: [PATCH v6 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index()

On June 30, 2024 11:40:02 PM PDT, Borislav Petkov <bp@...en8.de> wrote:
>On Sun, Jun 30, 2024 at 11:31:42PM -0700, H. Peter Anvin wrote:
>> Yes, all loads into a segment register are truncated to 16 bits.
>
>Right, but are we saying that somewhere explicitly or it is too obvious so
>that there's no need to?
>

I don't know. It is stated in a number of places, but I don't know if it is explicit in *this* specific context.