drm/i915: Use i915_gem_context_get_eb_vm in intel_context_set_gem

Since

commit ccbc1b9794
Author: Jason Ekstrand <jason@jlekstrand.net>
Date:   Thu Jul 8 10:48:30 2021 -0500

    drm/i915/gem: Don't allow changing the VM on running contexts (v4)

the gem_ctx->vm can't change anymore. Plus we always set the
intel_context->vm, so might as well use the helper we have for that.

This makes it very clear that we always overwrite intel_context->vm
for userspace contexts, since the default is gt->vm, which is
explicitly reserved for kernel context use. It would be good to split
things up a bit further and avoid any possibility for an accident
where we run kernel stuff in userspace vm or the other way round.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20210902142057.929669-8-daniel.vetter@ffwll.ch

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -791,16 +791,8 @@ static int intel_context_set_gem(struct intel_context *ce,
 
 	ce->ring_size = SZ_16K;
 
-	if (rcu_access_pointer(ctx->vm)) {
-		struct i915_address_space *vm;
-
-		rcu_read_lock();
-		vm = context_get_vm_rcu(ctx); /* hmm */
-		rcu_read_unlock();
-
 	i915_vm_put(ce->vm);
-		ce->vm = vm;
-	}
+	ce->vm = i915_gem_context_get_eb_vm(ctx);
 
 	if (ctx->sched.priority >= I915_PRIORITY_NORMAL &&
 	    intel_engine_has_timeslices(ce->engine) &&