linux-kernel - Re: [RFC][PATCH 4/7] x86/debug: Move historical SYSENTER junk into exc_debug

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Message-Id: <156769F5-0BCC-4FB8-A56D-0E92601F558A@amacapital.net>
Date:   Thu, 20 Aug 2020 09:43:15 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     peterz@...radead.org
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Brian Gerst <brgerst@...il.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kyle Huey <me@...ehuey.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Robert O'Callahan <rocallahan@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [RFC][PATCH 4/7] x86/debug: Move historical SYSENTER junk into exc_debug_kernel()



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

I’ve lost track of how many bugs QEMU and KVM have in this space.  Let’s keep it as a warning, but a bug. But let’s get rid of the totally bogus TIF_SINGLESTEP manipulation.