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

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Message-ID: <CALCETrW1VobMKcDU_zbvgy1DBe5j=iZUp165_q_NHS7+ZffG4g@mail.gmail.com>
Date:   Mon, 15 Jul 2019 12:44:42 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Uros Bizjak <ubizjak@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>
Subject: Re: [RFC PATCH, x86]: Disable CPA cache flush for selfsnoop targets

On Mon, Jul 15, 2019 at 12:39 PM Andi Kleen <ak@...ux.intel.com> wrote:
>
> > Right, we don't know where the PAT invocation comes from and whether they
> > are safe to omit flushing the cache. The module load code would be one
> > obvious candidate.
>
> Module load just changes the writable/executable status, right? That shouldn't
> need to flush in any case because it doesn't change the caching attributes.
>

Indeed.  module load should require a single TLB flush and no cache
flushes.  I don't think we're currently efficient enough to do it with
a single TLB flush, but we should be able to...