drm/i915: consider min_page_size when migrating

We can only force migrate an object if the existing object size is
compatible with the new destinations min_page_size for the region.
Currently we blow up with something like:

[ 2857.497462] kernel BUG at drivers/gpu/drm/i915/gt/intel_migrate.c:431!
[ 2857.497497] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[ 2857.497502] CPU: 1 PID: 8921 Comm: i915_selftest Tainted: G     U  W         5.18.0-rc1-drm-tip+ #27
[ 2857.497513] RIP: 0010:emit_pte.cold+0x11a/0x17e [i915]
[ 2857.497646] Code: 00 48 c7 c2 f0 cd c1 a0 48 c7 c7 e9 99 bd a0 e8 d2 77 5d e0 bf 01 00 00 00 e8 08 47 5d e0 31 f6 bf 09 00 00 00 e8 3c 7b 4d e0 <0f> 0b 48 c7 c1 e0 2a c5 a0 ba 34 00 00 00 48 c7 c6 00 ce c1 a0 48
[ 2857.497654] RSP: 0018:ffffc900000f7748 EFLAGS: 00010246
[ 2857.497658] RAX: 0000000000000000 RBX: ffffc900000f77c8 RCX: 0000000000000006
[ 2857.497662] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000009
[ 2857.497665] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
[ 2857.497668] R10: 0000000000022302 R11: ffff88846dea08f0 R12: 0000000000010000
[ 2857.497672] R13: 0000000001880000 R14: 000000000000081b R15: ffff888106b7c040
[ 2857.497675] FS:  00007f0d4c4e0600(0000) GS:ffff88845da80000(0000) knlGS:0000000000000000
[ 2857.497679] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2857.497682] CR2: 00007f113966c088 CR3: 0000000211e60003 CR4: 00000000003706e0
[ 2857.497686] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 2857.497689] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 2857.497692] Call Trace:
[ 2857.497694]  <TASK>
[ 2857.497697]  intel_context_migrate_copy+0x1e5/0x4f0 [i915]
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@linux.intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220420181613.70033-1-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -605,6 +605,9 @@ bool i915_gem_object_can_migrate(struct drm_i915_gem_object *obj,
 	if (!mr)
 		return false;
 
+	if (!IS_ALIGNED(obj->base.size, mr->min_page_size))
+		return false;
+
 	if (obj->mm.region == mr)
 		return true;
 

drivers/gpu/drm/i915/gem/selftests/i915_gem_migrate.c

@@ -47,14 +47,16 @@ static int igt_create_migrate(struct intel_gt *gt, enum intel_region_id src,
 {
 	struct drm_i915_private *i915 = gt->i915;
 	struct intel_memory_region *src_mr = i915->mm.regions[src];
+	struct intel_memory_region *dst_mr = i915->mm.regions[dst];
 	struct drm_i915_gem_object *obj;
 	struct i915_gem_ww_ctx ww;
 	int err = 0;
 
 	GEM_BUG_ON(!src_mr);
+	GEM_BUG_ON(!dst_mr);
 
 	/* Switch object backing-store on create */
-	obj = i915_gem_object_create_region(src_mr, PAGE_SIZE, 0, 0);
+	obj = i915_gem_object_create_region(src_mr, dst_mr->min_page_size, 0, 0);
 	if (IS_ERR(obj))
 		return PTR_ERR(obj);