linux-kernel - Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

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Message-ID: <CAJvTdK=VqyJ9io7bFeQDWfUtnG_iF=MqxVzPYDzEB8BJESgkyA@mail.gmail.com>
Date:   Fri, 21 May 2021 19:08:23 -0400
From:   Len Brown <lenb@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Dave Hansen via Libc-alpha <libc-alpha@...rceware.org>,
        Rich Felker <dalias@...c.org>,
        Linux API <linux-api@...r.kernel.org>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kyle Huey <me@...ehuey.com>, Borislav Petkov <bp@...en8.de>,
        Keno Fischer <keno@...iacomputing.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Willy Tarreau <w@....eu>
Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

On Fri, May 21, 2021 at 7:06 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 5/21/21 3:07 PM, Len Brown wrote:
> > My concern about synchronous allocation is that it will be very easy
> > to abuse.  programs and threads can ask for buffers they will never
> > use.  With on-demand allocation, we allocate buffers only if they are
> > actually needed.
>
> If someone wants to abuse the on-demand allocation, they will simply
> write a single bit to an AMX register.  That does *NOT* mean they will
> actually execute an instruction that actually uses AMX to do something
> meaningful.
>
> In the face of abuse, I think the two approaches are very similar.

I didn't mean "abuse" in terms of malicious resource hogging.
I meant "abuse" in terms of unnecessarily using resources out of laziness.