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From: Andy Lutomirski <luto@amacapital.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Brian Gerst <brgerst@gmail.com>, Juergen Gross <JGross@suse.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [patch 13/16] x86/entry: Move irqflags and context tracking to C for simple idtentries
Date: Wed, 26 Feb 2020 11:15:31 -0800	[thread overview]
Message-ID: <A4E714B9-ECBA-4984-986C-02B4EAF5018C@amacapital.net> (raw)
In-Reply-To: <20200226162811.GA18400@hirez.programming.kicks-ass.net>


> On Feb 26, 2020, at 8:28 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> On Wed, Feb 26, 2020 at 07:11:39AM -0800, Andy Lutomirski wrote:
> 
>> In some sense, this is a weakness of the magic macro approach.  Some
>> of the entries just want to have code that runs before all the entry
>> fixups.  This is an example of it.  So are the cr2 reads.  It can all
>> be made to work, but it's a bit gross.
> 
> Right. In my current pile (new patche since last posting) I also have
> one that makes #DB save-clear/restore DR7.
> 
> I got it early enough that only a watchpoint on the task stack can still
> screw us over, since I also included your patch that excludes
> cpu_entry_area.

Hmm. It would be nice to prevent watchpoints on the task stack, but that would need some trickery.  It could be done.

> 
> Pushing it earlier still would require calling into C from the entry
> stack, which I know is on your todo list, but we're not quite there yet.

Indeed.

This is my main objection to the DEFINE_IDTENTRY stuff. It’s *great* for the easy cases, but it’s not so great for the nasty cases. Maybe we should open code PF, MC, DB, etc.  (And kill the kvm special case for PF.  I have a working patch for that and I can send it.)

Anyway, this isn’t actually what I was concerned about. I meant DR6, not DR7.  Specifically, if we get traced too early in do_debug / exc_debug, we can recursively debug and clobber DR6.  The result will be incorrect behavior in the outer do_debug. We can fix this the same way we handle CR2.  I just haven’t done it on the existing entry code because it’s too messy.

  reply	other threads:[~2020-02-26 19:15 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-25 22:33 [patch 00/16] x86/entry: Consolidation - Part IV Thomas Gleixner
2020-02-25 22:33 ` [patch 01/16] x86/entry: Provide IDTENTRY_IST Thomas Gleixner
2020-02-25 22:33 ` [patch 02/16] x86/entry: Convert Machine Check to IDTENTRY_IST Thomas Gleixner
2020-02-25 22:33 ` [patch 03/16] x86/idtentry: Provide IDTENTRY_XEN for XEN/PV Thomas Gleixner
2020-02-25 22:33 ` [patch 04/16] x86/entry: Convert NMI to IDTENTRY_NMI Thomas Gleixner
2020-02-25 22:33 ` [patch 05/16] x86/entry: Convert Debug exception to IDTENTRY_DB Thomas Gleixner
2020-02-25 22:33 ` [patch 06/16] x86/entry/64: Remove error code clearing from #DB and #MCE ASM stub Thomas Gleixner
2020-02-25 22:33 ` [patch 07/16] x86/entry: Provide IDTRENTRY_NOIST variants for #DB and #MC Thomas Gleixner
2020-02-25 22:33 ` [patch 08/16] x86/entry: Implement user mode C entry points for #DB and #MCE Thomas Gleixner
2020-02-25 22:33 ` [patch 09/16] x86/entry: Provide IDTENTRY_DF Thomas Gleixner
2020-02-25 22:33 ` [patch 10/16] x86/entry: Convert double fault exception to IDTENTRY_DF Thomas Gleixner
2020-02-25 22:33 ` [patch 11/16] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY Thomas Gleixner
2020-02-25 22:33 ` [patch 12/16] x86/entry/64: Simplify idtentry_body Thomas Gleixner
2020-02-25 22:33 ` [patch 13/16] x86/entry: Move irqflags and context tracking to C for simple idtentries Thomas Gleixner
2020-02-26  8:05   ` Peter Zijlstra
2020-02-26  9:20     ` Peter Zijlstra
2020-02-26 15:11       ` Andy Lutomirski
2020-02-26 16:28         ` Peter Zijlstra
2020-02-26 19:15           ` Andy Lutomirski [this message]
2020-02-26 20:25             ` Thomas Gleixner
2020-02-26 17:05     ` Frederic Weisbecker
2020-02-26 17:09       ` Andy Lutomirski
2020-02-26 17:17         ` Frederic Weisbecker
2020-02-25 22:33 ` [patch 14/16] x86/entry: Provide IDTENTRY_CR2 Thomas Gleixner
2020-02-25 22:33 ` [patch 15/16] x86/entry: Switch page fault exceptions to idtentry_simple Thomas Gleixner
2020-03-05 21:51   ` Andy Lutomirski
2020-03-05 23:02     ` Thomas Gleixner
2020-02-25 22:33 ` [patch 16/16] x86/entry: Disable interrupts in IDTENTRY Thomas Gleixner
2020-02-26  9:23   ` Peter Zijlstra
2020-02-26 20:21     ` Thomas Gleixner
2020-02-27  8:41       ` Peter Zijlstra

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