linux-kernel - RE: [PATCH v2 6/6] x86/gsseg: use the LKGS instruction if available for load_gs

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Date:   Tue, 11 Oct 2022 17:12:40 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Brian Gerst <brgerst@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "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>
Subject: RE: [PATCH v2 6/6] x86/gsseg: use the LKGS instruction if available
 for load_gs_index()

> > +       asm_inline volatile("1:\n"
> > +                           ALTERNATIVE("call asm_load_gs_index\n",
> > +                                       _ASM_BYTES(0x3e) LKGS_DI,
> > +                                       X86_FEATURE_LKGS)
> > +                           _ASM_EXTABLE_TYPE_REG(1b, 1b, EX_TYPE_ZERO_REG,
> %k[sel])
> > +                           : ASM_CALL_CONSTRAINT
> > +                           : [sel] "D" (sel)
> 
> DI needs to be marked as input and output (+D), since the exception handler
> modifies it.

Good catch, I accidently removed it from the first version, will add it back.
Xin