linux-kernel - Re: [PATCH] x86/ia32: Do not modify the DPL bits for a null selector

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Message-ID: <80383055-7d9f-dea8-1883-91084d0d24a1@intel.com>
Date:   Thu, 6 Jul 2023 08:28:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, brgerst@...il.com,
        ebiederm@...ssion.com
Subject: Re: [PATCH] x86/ia32: Do not modify the DPL bits for a null selector

On 7/5/23 22:22, Xin Li wrote:
> When a null selector is to be loaded into a segment register,
> reload_segments() sets its DPL bits to 3. Later when an IRET
> instruction loads it, it zeros the segment register. The two
> operations offset each other to actually effect a nop.
> 
> Fix it by not modifying the DPL bits for a null selector.

So in the end, this is an optimization attempt?  Is there any other benefit?