drm/xe/uapi: Introduce a flag to disallow vm overcommit in fault mode

drm/xe/uapi: Introduce a flag to disallow vm overcommit in fault mode

Some compute applications may try to allocate device memory to probe
how much device memory is actually available, assuming that the
application will be the only one running on the particular GPU.

That strategy fails in fault mode since it allows VM overcommit.

While this could be resolved in user-space it's further complicated
by cgroups potentially restricting the amount of memory available
to the application.

Introduce a vm create flag, DRM_XE_VM_CREATE_NO_VM_OVERCOMMIT, that
allows fault mode to mimic the behaviour of !fault mode WRT this. It
blocks evicting same vm bos during VM_BIND processing. However,
it does *not* block evicting same-vm bos during pagefault
processing, preferring eviction rather than VM banning in
OOM situations.

Cc: John Falkowski <john.falkowski@intel.com>
Cc: Michal Mrozek <michal.mrozek@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260204153320.17989-1-thomas.hellstrom@linux.intel.com