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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [GIT PULL] x86/urgent for v5.11-rc7
Date:   Tue, 9 Feb 2021 10:26:37 -0800
Message-Id: <3C17D187-8691-4521-9B64-F42A0B514F13@amacapital.net>
References: <CAHk-=wgNXnmxjm+kK1ufjHfQPOBbuD5w3CTkSe0azF3NNWEHHQ@mail.gmail.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Borislav Petkov <bp@suse.de>,
        Dave Hansen <dave.hansen@intel.com>, x86-ml <x86@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        live-patching@vger.kernel.org
In-Reply-To: <CAHk-=wgNXnmxjm+kK1ufjHfQPOBbuD5w3CTkSe0azF3NNWEHHQ@mail.gmail.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Precedence: bulk


> On Feb 9, 2021, at 10:09 AM, Linus Torvalds <torvalds@linux-foundation.org=
> wrote:
>=20
> =EF=BB=BFOn Tue, Feb 9, 2021 at 8:55 AM Andy Lutomirski <luto@amacapital.n=
et> wrote:
>>=20
>> Or we hack up #CP to handle this case. I don=E2=80=99t quite know how I f=
eel about this.
>=20
> I think that's the sane model - if we've replaced the instruction with
> 'int3', and we end up getting #CP due to that, just do the #BP
> handling.
>=20
> Anything else would just be insanely complicated, I feel.

The other model is =E2=80=9Cdon=E2=80=99t do that then.=E2=80=9D

I suppose a nice property of patching ENDBR to INT3 is that, not only is it a=
tomic, but ENDBR is sort of a NOP, so we don=E2=80=99t need to replace the E=
NDBR with anything.

>=20
>             Linus