swiotlb: panic if nslabs is too small

Panic on purpose if nslabs is too small, in order to sync with the remap
retry logic.

In addition, print the number of bytes for tlb alloc failure.
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/swiotlb.c

@@ -242,6 +242,9 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
 	if (swiotlb_force_disable)
 		return;
 
+	if (nslabs < IO_TLB_MIN_SLABS)
+		panic("%s: nslabs = %lu too small\n", __func__, nslabs);
+
 	/*
 	 * By default allocate the bounce buffer memory from low memory, but
 	 * allow to pick a location everywhere for hypervisors with guest
@@ -254,7 +257,8 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
 	else
 		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
 	if (!tlb) {
-		pr_warn("%s: failed to allocate tlb structure\n", __func__);
+		pr_warn("%s: Failed to allocate %zu bytes tlb structure\n",
+			__func__, bytes);
 		return;
 	}