Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <625160026.9658.1523621809662.JavaMail.zimbra@efficios.com>
References: <20180412192800.15708-1-mathieu.desnoyers@efficios.com>
 <20180412192800.15708-13-mathieu.desnoyers@efficios.com> <CA+55aFxcJ2V_1BoW0Cct=Kkp7REkgiU_BTimGdmoFmWHaWaZ-g@mail.gmail.com>
 <1580648199.9463.1523563167045.JavaMail.zimbra@efficios.com>
 <CA+55aFwFUeNA6_0a1MOU-7VGzCw5T99cfVCPiyTpZQJdd6z=bw@mail.gmail.com> <625160026.9658.1523621809662.JavaMail.zimbra@efficios.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 13 Apr 2018 09:37:28 -0700
Message-ID: <CA+55aFwXCnnfrOjPj5SB=G34xgveo1jqNyf23YNt6jOKX_VdGw@mail.gmail.com>
Subject: Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Dave Watson <davejwatson@fb.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>,
        Paul Turner <pjt@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King <linux@arm.linux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Andrew Hunter <ahh@google.com>,
        Andi Kleen <andi@firstfloor.org>, Chris Lameter <cl@linux.com>,
        Ben Maurer <bmaurer@fb.com>, rostedt <rostedt@goodmis.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Apr 13, 2018 at 5:16 AM, Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
> The vmalloc space needed by cpu_opv is bound by the number of pages
> a cpu_opv call can touch.

No it's not.

You can have a thousand different processes doing cpu_opv at the same time.

A *single* cpu_opv may me limited toi "only" a megabyte, but I'm not
seeing any global limit anywhere.

In short, this looks like a guaranteed DoS approach to me.

                   Linus