linux-kernel - Re: [PATCH v2] x86/cpu: Use SERIALIZE in sync

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Message-ID: <2511352F-5D28-4337-A4A2-1B54073F1F72@zytor.com>
Date:   Tue, 04 Aug 2020 22:10:22 -0700
From:   hpa@...or.com
To:     Borislav Petkov <bp@...en8.de>
CC:     Borislav Petkov <bp@...e.de>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.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 v2] x86/cpu: Use SERIALIZE in sync_core() when available

On August 4, 2020 10:08:08 PM PDT, Borislav Petkov <bp@...en8.de> wrote:
>On Tue, Aug 04, 2020 at 09:58:25PM -0700, hpa@...or.com wrote:
>> Because why use an alternative to jump over one instruction?
>>
>> I personally would prefer to have the IRET put out of line
>
>Can't yet - SERIALIZE CPUs are a minority at the moment.
>
>> and have the call/jmp replaced by SERIALIZE inline.
>
>Well, we could do:
>
>	alternative_io("... IRET bunch", __ASM_SERIALIZE,
>X86_FEATURE_SERIALIZE, ...);
>
>and avoid all kinds of jumping. Alternatives get padded so there
>would be a couple of NOPs following when SERIALIZE gets patched in
>but it shouldn't be a problem. I guess one needs to look at what gcc
>generates...

I didn't say behind a trap. IRET is a control transfer instruction, and slow, so putting it out of line really isn't unreasonable. Can even do a call to a common handler.
-- 
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