linux-kernel - Re: [RFC PATCH, x86]: Disable CPA cache flush for selfsnoop targets

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Message-ID: <CALCETrXKgVMiqSfaWoBoM+WCZGHDihV8frSOdG5BFsRr2=mGJw@mail.gmail.com>
Date:   Thu, 11 Jul 2019 07:39:28 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Uros Bizjak <ubizjak@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH, x86]: Disable CPA cache flush for selfsnoop targets

On Thu, Jul 11, 2019 at 1:13 AM Uros Bizjak <ubizjak@...il.com> wrote:
>
> Recent patch [1] disabled a self-snoop feature on a list of processor
> models with a known errata, so we are confident that the feature
> should work on remaining models also for other purposes than to speed
> up MTRR programming.
>
> I would like to resurrect an old patch [2] that avoids calling clflush
> and wbinvd
> to invalidate caches when CPU supports selfsnoop.

The big question here is: what are all the reasons that we might need
to flush?  Certainly, for stuff like SEV and MKTME, we need to flush
regardless of any self-snoop capability.