On 11/08/16 17:02, Arnd Bergmann wrote:
On Thursday, August 11, 2016 12:02:42 AM CEST Russell King - ARM Linux wrote:
On Wed, Aug 10, 2016 at 09:31:05PM +0200, Arnd Bergmann wrote:
On Wednesday, August 10, 2016 11:12:53 AM CEST Russell King - ARM Linux wrote:
There's the TLS emulation too, but that writes via the vectors mapping
at 0xffff0ff0.
Ok, so that should be safe. Can we change the fiq code to also use the
high mapping and then take the __ro_after_init patch on top?
We can't - if the kernel is configured without the kuser helpers in
the vectors page, it's mapped read-only. I'm not sure what the
intersection is between platforms that can have FIQs and platforms
that can disable the kuser helpers.
From Kconfig logic and callers of set_fiq_handler(), theoretically
there is just i.MX3, but I think they never use fiq in their
audio drivers in practice already, and Mark Brown mentioned
that we could remove fiq support in the imx audio driver (don't
remember the details at the moment).
If we can prove that i.MX3 PCM FIQ support is never used, then the
intersection is empty, and all machines that use FIQ require kuser
helpers.
This may change with Daniel Thompson's patches that use the FIQ
for NMI backtrace.
It shouldn't do!
All the work I did (and am, very slowly, still doing) worked by using
the default FIQ handler provided at boot time to jump into the perf code.
Nothing I have done or plan to do needs set_fiq_handler() to remain
functional.
Likewise, nothing I have done should cause set_fiq_handler() to stop
working for people who do still use it. FWIW I got the impression over
the last few years that the most significant uses of FIQ on modern
systems are out-of-tree uses who have designed custom FPGA hardware (and
presumably designed them with very short FIFOs).
Daniel.
--
To unsubscribe from this list: send the line "unsubscribe linux-arch" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
