Hi Ricardo,

On 15/06/18 03:12, Ricardo Neri wrote:

On Wed, Jun 13, 2018 at 11:06:25AM +0100, Marc Zyngier wrote:

quoted

On 13/06/18 10:20, Thomas Gleixner wrote:

quoted

On Wed, 13 Jun 2018, Julien Thierry wrote:

quoted

On 13/06/18 09:34, Peter Zijlstra wrote:

quoted

On Tue, Jun 12, 2018 at 05:57:23PM -0700, Ricardo Neri wrote:

quoted

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 5426627..dbc5e02 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h

@@ -61,6 +61,8 @@
    *                interrupt handler after suspending interrupts. For

system
    *                wakeup devices users need to implement wakeup
detection in
    *                their interrupt handlers.
+ * IRQF_DELIVER_AS_NMI - Configure interrupt to be delivered as
non-maskable, if
+ *                supported by the chip.
    */

NAK on the first 6 patches. You really _REALLY_ don't want to expose
NMIs to this level.

I've been working on something similar on arm64 side, and effectively the one
thing that might be common to arm64 and intel is the interface to set an
interrupt as NMI. So I guess it would be nice to agree on the right approach
for this.

The way I did it was by introducing a new irq_state and let the irqchip driver
handle most of the work (if it supports that state):

https://lkml.org/lkml/2018/5/25/181

This has not been ACKed nor NAKed. So I am just asking whether this is a more
suitable approach, and if not, is there any suggestions on how to do this?

I really didn't pay attention to that as it's burried in the GIC/ARM series
which is usually Marc's playground.

I'm working my way through it ATM now that I have some brain cycles back.

quoted

Adding NMI delivery support at low level architecture irq chip level is
perfectly fine, but the exposure of that needs to be restricted very
much. Adding it to the generic interrupt control interfaces is not going to
happen. That's doomed to begin with and a complete abuse of the interface
as the handler can not ever be used for that.

I can only agree with that. Allowing random driver to use request_irq()
to make anything an NMI ultimately turns it into a complete mess ("hey,
NMI is *faster*, let's use that"), and a potential source of horrible
deadlocks.

What I'd find more palatable is a way for an irqchip to be able to
prioritize some interrupts based on a set of architecturally-defined
requirements, and a separate NMI requesting/handling framework that is
separate from the IRQ API, as the overall requirements are likely to
completely different.

It shouldn't have to be nearly as complex as the IRQ API, and require
much stricter requirements in terms of what you can do there (flow
handling should definitely be different).

Marc, Julien, do you plan to actively work on this? Would you mind keeping
me in the loop? I also need this work for this watchdog. In the meantime,
I will go through Julien's patches and try to adapt it to my work.

We are going to work on this and of course your input is most welcome to 
make sure we have an interface usable across different architectures.

In my patches, I'm not sure there is much to adapt to your work as most 
of it is arch specific (although I wont say no to another pair of eyes 
looking at them). From what I've seen of your patches, the point where 
we converge is that need for some code to be able to tell the irqchip "I 
want that particular interrupt line to be treated/setup as an NMI".

We'll make sure to keep you in the loop for discussions/suggestions on this.

Thanks,

-- 
Julien Thierry