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

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Date:   Wed, 5 Aug 2020 07:08:08 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     hpa@...or.com
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 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...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette