[Intel-gfx] [PATCH] RFC drm/i915/gem: Allow creation of contexts with an 'empty' VM

[Chris Wilson]

Quoting Chris Wilson (2020-04-21 17:41:30)
> Normally when we create a new context, and a new ppGTT to go with it, we
> point all the unused pages in the ppGTT to a 'safe' scratch page. Any
> inadvertent access outside of the declared user's area will result in a
> read/write to scratch instead. However, sometimes it is preferrable to
> that to cause a fault instead. This does not trap execution of the
> faulting batch, but it does record the error:
> 
> FAULT_TLB_DATA: 0x00000000 0x00000004
>     Address 0x0000000000004000 PPGTT
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> ---
> The name and value semantics are horrendous. The non-trapping behaviour
> is also less than ideal. Worth it?

Note that we can ask for an interrupt on a page access error, however it
is a 'validation' error and we get an interrupt for every single access
and NOOP fixup (the single bit for all classes of validation errors).
They were quite frequent.
-Chris