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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Xin Li' <xin3.li@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>
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        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
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        "chang.seok.bae@intel.com" <chang.seok.bae@intel.com>
Subject: RE: [PATCH v3 3/6] x86/gsseg: make asm_load_gs_index() take an u16
Thread-Topic: [PATCH v3 3/6] x86/gsseg: make asm_load_gs_index() take an u16
Thread-Index: AQHY30Gyx3nzbyqdTEiu3El5Q4Xlsa4N0NzA
Date:   Fri, 14 Oct 2022 12:28:25 +0000
Message-ID: <86f60a8edf0e458c86cd84970364cfa2@AcuMS.aculab.com>
References: <20221013200134.1487-1-xin3.li@intel.com>
 <20221013200134.1487-4-xin3.li@intel.com>
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From: Xin Li
> Sent: 13 October 2022 21:02
> 
> From: "H. Peter Anvin (Intel)" <hpa@zytor.com>
> 
> Let gcc know that only the low 16 bits of load_gs_index() argument
> actually matter. It might allow it to create slightly better
> code. However, do not propagate this into the prototypes of functions
> that end up being paravirtualized, to avoid unnecessary changes.

Using u16 will almost always make the code worse.
At some point the value has to be masked and/or extended
to ensure an out of range value doesn't appear in
a register.

	David

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