linux-kernel - RE: [PATCH v9 09/17] x86/split_lock: Handle #AC exception for split lock

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Message-ID: <053924e2d08b4744b9fd10337e83ab2d@AcuMS.aculab.com>
Date:   Wed, 16 Oct 2019 14:14:45 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Paolo Bonzini' <pbonzini@...hat.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Dave Hansen" <dave.hansen@...el.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [PATCH v9 09/17] x86/split_lock: Handle #AC exception for split
 lock

For the smt case, can you make #AC enable a property of the process?
Then disable it on the core if either smt process requires it be disabled?

This would mean that is a 'mixed environment' not all split accesses
would actually generate #AC - but enough would to detect broken code
that doesn't have #AC explicitly disabled.

I'm not sure you'd want a guest to flip #AC enable based on the process
it is scheduling, but it might work for the base metal scheduler.

	David

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