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;
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
From:   Andy Lutomirski <luto@amacapital.net>
Mime-Version: 1.0 (1.0)
Subject: Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken
Date:   Sun, 31 Jan 2021 14:04:44 -0800
Message-Id: <0456DEB3-2EA6-4CA6-AA59-E5E1D8F1A77A@amacapital.net>
References: <CAHk-=wgeG7WP_vxho_bfENK3rYP9zUF0_ZjA1X3OftERrs_j2w@mail.gmail.com>
Cc:     Kyle Huey <me@kylehuey.com>, Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        open list <linux-kernel@vger.kernel.org>,
        Robert O'Callahan <rocallahan@gmail.com>
In-Reply-To: <CAHk-=wgeG7WP_vxho_bfENK3rYP9zUF0_ZjA1X3OftERrs_j2w@mail.gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Precedence: bulk


> On Jan 31, 2021, at 1:30 PM, Linus Torvalds <torvalds@linux-foundation.org=
> wrote:
>=20
> =EF=BB=BFBtw Kyle, do you have a good simple test-case for this? Clearly t=
his
> is some weird special case use, and regular single-stepping works
> fine.
>=20
>=20

Indeed, and I have tests for this.

TBH, the TIF_SINGLESTEP code makes no sense, and I think it has at least thr=
ee overloaded meanings. I can try to look in a bit.  I=E2=80=99ve mostly avo=
ided breaking it in the past, but that doesn=E2=80=99t mean I understand the=
 original intent.=