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Date:   Mon, 27 Jul 2020 10:36:19 +0200
From:   peterz@infradead.org
To:     hpa@zytor.com
Cc:     Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
        Andy Lutomirski <luto@kernel.org>, x86@kernel.org,
        Dave Hansen <dave.hansen@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Cathy Zhang <cathy.zhang@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Kyung Min Park <kyung.min.park@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        linux-kernel@vger.kernel.org,
        Ricardo Neri <ricardo.neri@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-edac@vger.kernel.org
Subject: Re: [PATCH 4/4] x86/cpu: Use SERIALIZE in sync_core() when available
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On Sun, Jul 26, 2020 at 10:55:15PM -0700, hpa@zytor.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.