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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [RFC][PATCH 4/7] x86/debug: Move historical SYSENTER junk into exc_debug_kernel()
Date:   Thu, 20 Aug 2020 09:43:15 -0700
Message-Id: <156769F5-0BCC-4FB8-A56D-0E92601F558A@amacapital.net>
References: <20200820163453.GE1362448@hirez.programming.kicks-ass.net>
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Brian Gerst <brgerst@gmail.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kyle Huey <me@kylehuey.com>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Robert O'Callahan <rocallahan@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        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>,
        Andy Lutomirski <luto@kernel.org>
In-Reply-To: <20200820163453.GE1362448@hirez.programming.kicks-ass.net>
To:     peterz@infradead.org
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Aug 20, 2020, at 9:35 AM, peterz@infradead.org wrote:
>=20
> =EF=BB=BFOn Thu, Aug 20, 2020 at 11:17:29AM -0500, Josh Poimboeuf wrote:
>> On Thu, Aug 20, 2020 at 05:21:11PM +0200, peterz@infradead.org wrote:
>=20
>>> qemu-gdb stub should eat the event before it lands in the guest
>>=20
>> Are we sure about that?  I triggered the warning just now, stepping
>> through the debug handler.
>=20
> Not sure at all, that's what seemed reasonable, but since when did that
> stop virt ;-)
>=20
> Also, can you trigger that same with upstream? Because I suspect this
> ought to tickle the old code too.

I=E2=80=99ve lost track of how many bugs QEMU and KVM have in this space.  L=
et=E2=80=99s keep it as a warning, but a bug. But let=E2=80=99s get rid of t=
he totally bogus TIF_SINGLESTEP manipulation.=