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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [patch V4 part 3 17/29] x86/entry: Convert Invalid Opcode exception to IDTENTRY
Date:   Thu, 14 May 2020 08:00:10 -0700
Message-Id: <D75719A6-44E5-4F6F-8308-58DD2E74374D@amacapital.net>
References: <87k11ezog1.fsf@nanos.tec.linutronix.de>
Cc:     Andy Lutomirski <luto@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <JGross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>
In-Reply-To: <87k11ezog1.fsf@nanos.tec.linutronix.de>
To:     Thomas Gleixner <tglx@linutronix.de>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On May 14, 2020, at 5:33 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
>=20
> =EF=BB=BFAndy Lutomirski <luto@kernel.org> writes:
>=20
>>> On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner <tglx@linutronix.de> wrot=
e:
>>>=20
>>> From: Thomas Gleixner <tglx@linutronix.de>
>>>=20
>>> Convert #UD to IDTENTRY:
>>>  - Implement the C entry point with DEFINE_IDTENTRY
>>>  - Emit the ASM stub with DECLARE_IDTENTRY
>>>  - Remove the ASM idtentry in 64bit
>>>  - Remove the open coded ASM entry code in 32bit
>>>  - Fixup the XEN/PV code
>>>  - Fixup the FOOF bug call in fault.c
>>>  - Remove the old prototyoes
>>>=20
>>> No functional change.
>>=20
>> I think there *is* a functional change:
>>=20
>>=20
>>> --- a/arch/x86/mm/fault.c
>>> +++ b/arch/x86/mm/fault.c
>>> @@ -567,7 +567,7 @@ static int is_f00f_bug(struct pt_regs *r
>>>                nr =3D (address - idt_descr.address) >> 3;
>>>=20
>>>                if (nr =3D=3D 6) {
>>> -                       do_invalid_op(regs, 0);
>>> +                       handle_invalid_op(regs);
>>=20
>> I suspect the old code was wrong and no one noticed because no one has
>> a F00F-buggy machine any more.
>=20
> I don't think so. It's really just the same thing. The old #UD C
> function was:
>=20
> void do_invalid_op(struct pt_regs *regs, long error_code)
> {
>    do_error_trap(regs, error_code, "invalid opcode", X86_TRAP_UD,
>                      SIGILL, ILL_ILLOPN, (void __user *)uprobe_get_trap_ad=
dr(regs));
> }
>=20
> after expanding the DO_ERROR() muck.
>=20
> The new one does:
>=20
> void handle_invalid_op(struct pt_regs *regs)
> {
>    do_error_trap(regs, 0, "invalid opcode", X86_TRAP_UD, SIGILL,
>              ILL_ILLOPN, error_get_trap_addr(regs));
> }
>=20
> which is exactly the same except for the error code being hardcoded to
> zero in handle_invalid_op() because #UD does not have one.
>=20
>> So maybe document that you fixed up the F00F bug, too.  Otherwise:
>=20
> Not sure what to document :)

Duh, right, never mind.  Here I was thinking the old C handlers did all the e=
ntry/exit work.

>=20
> Thanks,
>=20
>        tglx