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Message-ID: <80383055-7d9f-dea8-1883-91084d0d24a1@intel.com>
Date:   Thu, 6 Jul 2023 08:28:07 -0700
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Subject: Re: [PATCH] x86/ia32: Do not modify the DPL bits for a null selector
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To:     Xin Li <xin3.li@intel.com>, linux-kernel@vger.kernel.org,
        x86@kernel.org
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com, brgerst@gmail.com,
        ebiederm@xmission.com
References: <20230706052231.2183-1-xin3.li@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20230706052231.2183-1-xin3.li@intel.com>
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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?