Re: [PATCH v2 01/18] x86/entry/64: Fix entry_SYSCALL_64_after_hwframe IRQ tracing

From: Ingo Molnar
Date: Wed Nov 22 2017 - 00:35:40 EST

* Andy Lutomirski <luto@xxxxxxxxxx> 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

> Move TRACE_IRQS_OFF below the label.