Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <1631147036-13597-1-git-send-email-prakash.sangappa@oracle.com>
 <CAFTs51VDUPWu=r9d=ThABc-Z6wCwTOC+jKDCq=Jk8Pfid61xyQ@mail.gmail.com>
 <CAPNVh5dsN0LPHg6TJ_MO2XKtpTEe0n4Y6+HjwERJPSrb2J0cbg@mail.gmail.com>
 <3591AC6D-45D2-476A-80B1-46BFA1742602@oracle.com> <CAPNVh5fMUQCa37iprcAykgkHzY5Rj8DSiwtZBU6FbnzjOv8ciw@mail.gmail.com>
 <CAG48ez1sPjPYePmXTgtFbaj6_0yY0Z_bGw+apwO_zTV-qwftSA@mail.gmail.com>
 <CAPNVh5fP-QnziX7NpYqKv+0Ha8-prhvTHiCbUB0jx+_P36QUGg@mail.gmail.com> <6A88B271-EC5E-46B7-8D60-A7543635FDC5@oracle.com>
In-Reply-To: <6A88B271-EC5E-46B7-8D60-A7543635FDC5@oracle.com>
From:   Peter Oskolkov <posk@google.com>
Date:   Mon, 13 Sep 2021 11:00:06 -0700
Message-ID: <CAPNVh5fQXB7tLi=tKyabmScZge53PwzQ3kqP2ASE+3DD+eTdGg@mail.gmail.com>
Subject: Re: [RESEND RFC PATCH 0/3] Provide fast access to thread specific data
To:     Prakash Sangappa <prakash.sangappa@oracle.com>
Cc:     Jann Horn <jannh@google.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Paul Turner <pjt@google.com>,
        Peter Oskolkov <posk@posk.io>,
        Peter Zijlstra <peterz@infradead.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Sep 13, 2021 at 10:36 AM Prakash Sangappa
<prakash.sangappa@oracle.com> wrote:

[...]

> > This sounds, again, as if the kernel should be aware of the kind of
> > items being allocated; having a more generic mechanism of allocating
> > pinned memory for the userspace to use at its discretion would be more
> > generally useful, I think. But how then the kernel/system should be
> > protected from a buggy or malicious process trying to grab too much?
> >
> > One option would be to have a generic in-kernel mechanism for this,
> > but expose it to the userspace via domain-specific syscalls that do
> > the accounting you hint at. This sounds a bit like an over-engineered
> > solution, though=E2=80=A6
>
>
> What will this pinned memory be used for in your use case,
> can you explain?

For userspace scheduling, to share thread/task state information
between the kernel and the userspace. This memory will be allocated
per task/thread; both the kernel and the userspace will write to the
shared memory, and these reads/writes will happen not only in the
memory regions belonging to the "current" task/thread, but also to
remote tasks/threads.

Somewhat detailed doc/rst is here:
https://lore.kernel.org/lkml/20210908184905.163787-5-posk@google.com/