linux-kernel - Re: [PATCH 4/4] x86/cpu: Use SERIALIZE in sync

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Message-ID: <49251CFA-8AC3-462D-A60F-0337593BE9CD@zytor.com>
Date:   Mon, 27 Jul 2020 05:49:28 -0700
From:   hpa@...or.com
To:     peterz@...radead.org
CC:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Cathy Zhang <cathy.zhang@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Kyung Min Park <kyung.min.park@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-edac@...r.kernel.org
Subject: Re: [PATCH 4/4] x86/cpu: Use SERIALIZE in sync_core() when available

On July 27, 2020 1:36:19 AM PDT, peterz@...radead.org wrote:
>On Sun, Jul 26, 2020 at 10:55:15PM -0700, hpa@...or.com wrote:
>> For a really overenginered solution, but which might perform
>> unnecessary poorly on existing hardware:
>> 
>> asm volatile("1: .byte 0xf, 0x1, 0xe8; 2:"
>>                         _ASM_EXTABLE(1b,2b));
>
>Ha! cute, you take an #UD ?
>
>We could optimize the #UD exception handler for this I suppose, but
>that
>makes it an even worse hack. The simple alternative() seems like a much
>simpler approach.

If this is in any way performance critical, then no :) Taking the #UD has the cute property that we end up IRET on the way back, so we don't even need a fix-up path.


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