Am 09.02.21 um 15:30 schrieb Andrey Grodzovsky:
[SNIP]
Question - Why can't we just set those PTEs to point to system
memory (another RO dummy page)
filled with 1s ?
Then writes are not discarded. E.g. the 1s would change to something
else.
Christian.
I see but, what about marking the mappings as RO and discarding the
write access page faults continuously until the device is finalized ?
Regarding using an unused range behind the upper bridge as Daniel
suggested, I wonder will this interfere with
the upcoming feature to support BARs movement during hot plug -
https://www.spinics.net/lists/linux-pci/msg103195.html ?
In the picture in my head the address will never be used.
But it doesn't even needs to be an unused range of the root bridge. That
one is usually stuffed full by the BIOS.
For my BAR resize work I looked at quite a bunch of NB documentation. At
least for AMD CPUs we should always have an MMIO address which is never
ever used. That makes this platform/CPU dependent, but the code is just
minimal.
The really really nice thing about this approach is that you could unit
test and audit the code for problems even without *real* hotplug
hardware. E.g. we can swap the kernel PTEs and see how the whole power
and display code reacts to that etc....
Christian.
Andrey
Andrey
Christian.
It's a nifty idea indeed otherwise ...
-Daniel
Regards,
Christian.
But ugh ...
Otoh validating an entire driver like amdgpu without such a
trick
against 0xff reads is practically impossible. So maybe you
need to add
this as one of the tasks here?
Or I could just for validation purposes return ~0 from all
reg reads in the code
and ignore writes if drm_dev_unplugged, this could already
easily validate a big
portion of the code flow under such scenario.
Hm yeah if your really wrap them all, that should work too.
Since
iommappings have __iomem pointer type, as long as amdgpu is
sparse
warning free, should be doable to guarantee this.
Problem is that ~0 is not always a valid register value.
You would need to audit every register read that it doesn't
use the returned
value blindly as index or similar. That is quite a bit of work.
Yeah that's the entire crux here :-/
-Daniel
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
