drm/ttm: Make the call to ttm_tt_populate() interruptible when faulting

When swapping in, or under memory pressure ttm_tt_populate() may sleep
for a substantiable amount of time. Allow interrupts during the sleep.
This will also allow us to inject -EINTR errors during swapin in upcoming
patches.

Also avoid returning VM_FAULT_OOM, since that will confuse the core
mm, making it print out a confused message and retrying the fault.
Return VM_FAULT_SIGBUS also under OOM conditions.

Signed-off-by: Thomas Hellström <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/ttm/ttm_bo_vm.c

···
 	prot = ttm_io_prot(bo, bo->resource, prot);
 	if (!bo->resource->bus.is_iomem) {
 		struct ttm_operation_ctx ctx = {
-			.interruptible = false,
+			.interruptible = true,
 			.no_wait_gpu = false,
 			.force_alloc = true
 		};
 
 		ttm = bo->ttm;
-		if (ttm_tt_populate(bdev, bo->ttm, &ctx))
-			return VM_FAULT_OOM;
+		err = ttm_tt_populate(bdev, bo->ttm, &ctx);
+		if (err) {
+			if (err == -EINTR || err == -ERESTARTSYS ||
+			    err == -EAGAIN)
+				return VM_FAULT_NOPAGE;
+
+			pr_debug("TTM fault hit %pe.\n", ERR_PTR(err));
+			return VM_FAULT_SIGBUS;
+		}
 	} else {
 		/* Iomem should not be marked encrypted */
 		prot = pgprot_decrypted(prot);