linux-kernel - RE: [PATCH v3 3/6] x86/gsseg: make asm_load_gs

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Message-ID: <BN6PR1101MB216120D24ECD8A5C7DB9C64BA8279@BN6PR1101MB2161.namprd11.prod.outlook.com>
Date:   Sat, 15 Oct 2022 00:13:47 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "brgerst@...il.com" <brgerst@...il.com>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>
Subject: RE: [PATCH v3 3/6] x86/gsseg: make asm_load_gs_index() take an u16

> >
> > From: "H. Peter Anvin (Intel)" <hpa@...or.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.

Any potential issue with this patch set?

> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1
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