linux-kernel - Re: [PATCH v2 1/3] x86/entry/64: Refactor IRQ stacks and make them NMI-safe

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Message-ID: <CALCETrXZTK1J4Sea4J+a3O+6N6FtpLard80794r=rBfE0Zm7Vg@mail.gmail.com>
Date:	Wed, 19 Aug 2015 08:50:25 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, Willy Tarreau <w@....eu>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 1/3] x86/entry/64: Refactor IRQ stacks and make them NMI-safe

On Mon, Aug 17, 2015 at 4:18 AM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Sat, Jul 25, 2015 at 8:57 AM, Andy Lutomirski <luto@...nel.org> wrote:
>> This will allow IRQ stacks to nest inside NMIs or similar entries
>> that can happen during IRQ stack setup or teardown.
>>
>> The Xen code here has a confusing comment.
>>
>> The new macros won't work correctly if they're invoked with IRQs on.
>> Add a check under CONFIG_DEBUG_ENTRY to detect that.
>>
>
>> +/*
>> + * Enters the IRQ stack if we're not already using it.  NMI-safe.  Clobbers
>> + * flags and puts old RSP into old_rsp, and leaves all other GPRs alone.
>> + * Requires kernel GSBASE.
>> + *
>> + * The invariant is that, if irq_count != 1, then the IRQ stack is in use.
>> + */
>
> I might be wrong, but shouldn't be this read as 'if irq_count != -1' ?
>

Indeed.  Will fix for the next version.

--Andy
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