linux-kernel - Re: [PATCH v2 01/18] x86/entry/64: Fix entry_SYSCALL_64_after

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Date:   Wed, 22 Nov 2017 06:35:27 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, stable@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH v2 01/18] x86/entry/64: Fix
 entry_SYSCALL_64_after_hwframe IRQ tracing


* Andy Lutomirski <luto@...nel.org> wrote:

> When I added entry_SYSCALL_64_after_hwframe, I left TRACE_IRQS_OFF
> before it.  This means that users of entry_SYSCALL_64_after_hwframe
> were responsible for invoking TRACE_IRQS_OFF, and the one and only
> user (added in the same commit) got it wrong.
> 
> I think this would manifest as a warning if a Xen PV guest with
> CONFIG_DEBUG_LOCKDEP=y were used with context tracking.  (The
> context tracking bit is to cause lockdep to get invoked before we
> turn IRQs back on.)  I haven't tested that for real yet because I
> can't get a kernel configured like that to boot at all on Xen PV.
> I've reported it upstream.  The problem seems to be that Xen PV is
> missing early #UD handling, is hitting some WARN, and we rely on

JFYI, seems the changelog got truncated at this point - I simply removed that 
partial sentence as I suppose those details will be explained in the Xen fix 
anyway.

> Move TRACE_IRQS_OFF below the label.

Thanks,

	Ingo