On Sat, Feb 13, 2021 at 12:00 AM Song Bao Hua (Barry Song)
<song.bao.hua@xxxxxxxxxxxxx> wrote:
-----Original Message-----
From: Arnd Bergmann [mailto:arnd@xxxxxxxxxx]
Sent: Saturday, February 13, 2021 11:34 AM
To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx>
Cc: tglx@xxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; arnd@xxxxxxxx;
geert@xxxxxxxxxxxxxx; funaho@xxxxxxxxx; philb@xxxxxxx; corbet@xxxxxxx;
mingo@xxxxxxxxxx; linux-m68k@xxxxxxxxxxxxxxxxxxxx;
fthain@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [RFC] IRQ handlers run with some high-priority interrupts(not NMI)
enabled on some platform
On Fri, Feb 12, 2021 at 2:18 AM Song Bao Hua (Barry Song)
<song.bao.hua@xxxxxxxxxxxxx> wrote:
So I am requesting comments on:
1. are we expecting all interrupts except NMI to be disabled in irq handler,
or do we actually allow some high-priority interrupts between low and NMI
to
come in some platforms?
I tried to come to an answer but this does not seem particularly well-defined.
There are a few things I noticed:
- going through the local_irq_save()/restore() implementations on all
architectures, I did not find any other ones besides m68k that leave
high-priority interrupts enabled. I did see that at least alpha and openrisc
are designed to support that in hardware, but the code just leaves the
interrupts disabled.
The case is a little different. Explicit local_irq_save() does disable all
high priority interrupts on m68k. The only difference is arch_irqs_disabled()
of m68k will return true while low-priority interrupts are masked and high
-priority are still open. M68k's hardIRQ also runs in this context with high
priority interrupts enabled.
My point was that on most other architectures, local_irq_save()/restore()
always disables/enables all interrupts, while on m68k it restores the
specific level they were on before. On alpha, it does the same as on m68k,
but then the top-level interrupt handler just disables them all before calling
into any other code.
It's possible that I missed some other implementation doing the same
as m68k, as this code is fairly subtle on some architectures.
Arnd
