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

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Date:   Fri, 21 May 2021 16:06:04 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Len Brown <lenb@...nel.org>, Thomas Gleixner <tglx@...utronix.de>
Cc:     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 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.