MIME-Version: 1.0
References: <CAHk-=wgbm1rjkSs0w+dVJJzzK2M1No=j419c+i7T4V4ky2skOw@mail.gmail.com>
 <20230302083025.khqdizrnjkzs2lt6@wittgenstein> <CAHk-=wivxuLSE4ESRYv_=e8wXrD0GEjFQmUYnHKyR1iTDTeDwg@mail.gmail.com>
 <CAGudoHF9WKoKhKRHOH_yMsPnX+8Lh0fXe+y-K26mVR0gajEhaQ@mail.gmail.com>
 <ZADoeOiJs6BRLUSd@ZenIV> <CAGudoHFhnJ1z-81FKYpzfDmvcWFeHNkKGdr00CkuH5WJa2FAMQ@mail.gmail.com>
 <CAHk-=wjp5fMupRwnROtC5Yn+MVLA7v=J+_QJSi1rr3qAjdsfXw@mail.gmail.com>
 <CAHk-=wi11ZbOBdMR5hQDz0x0NNZ9gM-4SxXxK-7R3_yh7e10rQ@mail.gmail.com>
 <ZAD21ZEiB2V9Ttto@ZenIV> <6400fedb.170a0220.ece29.04b8@mx.google.com>
 <ZAEC3LN6oUe6BKSN@ZenIV> <CAG_fn=UQEuvJ9WXou_sW3moHcVQZJ9NvJ5McNcsYE8xw_WEYGw@mail.gmail.com>
 <CAGudoHFqNdXDJM2uCQ9m7LzP0pAx=iVj1WBnKc4k9Ky1Xf5XmQ@mail.gmail.com>
 <CAHk-=wh-eTh=4g28Ec5W4pHNTaCSZWJdxVj4BH2sNE2hAA+cww@mail.gmail.com> <CAGudoHG+anGcO1XePmLjb+Hatr4VQMiZ2FufXs8hT3JrHyGMAw@mail.gmail.com>
In-Reply-To: <CAGudoHG+anGcO1XePmLjb+Hatr4VQMiZ2FufXs8hT3JrHyGMAw@mail.gmail.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 3 Mar 2023 12:08:01 -0800
Message-ID: <CAHk-=wjy_q9t4APgug9q-EBMRKAybXt9DQbyM9Egsh=F+0k2Mg@mail.gmail.com>
Subject: Re: [PATCH v3 2/2] vfs: avoid duplicating creds in faccessat if possible
To:     Mateusz Guzik <mjguzik@gmail.com>
Cc:     Alexander Potapenko <glider@google.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Kees Cook <keescook@chromium.org>,
        Eric Biggers <ebiggers@google.com>,
        Christian Brauner <brauner@kernel.org>, serge@hallyn.com,
        paul@paul-moore.com, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Mar 3, 2023 at 11:37=E2=80=AFAM Mateusz Guzik <mjguzik@gmail.com> w=
rote:
>
> I mentioned in the previous e-mail that memset is used a lot even
> without the problematic opt and even have shown size distribution of
> what's getting passed there.

Well, I *have* been pushing Intel to try to fix memcpy and memset for
over two decades by now, but with FSRM I haven't actually seen the
huge problems any more.

It may just be that the loads I look at don't have issues (or the
machines I've done profiles on don't tend to show them as much).

Hmm. Just re-did my usual kernel profile. It may also be that
something has changed. I do see "clear_page" at the top, but yes,
memset is higher up than I remembered.

I actually used to have the reverse of your hack for this - I've had
various hacks over the year that made memcpy and memset be inlined
"rep movs/stos", which (along with inlined spinlocks) is a great way
to see the _culprit_ (without having to deal with the call chains -
which always get done the wrong way around imnsho).

            Linus