iommu/pages: Move the __GFP_HIGHMEM checks into the common code

The entire allocator API is built around using the kernel virtual address,
it is illegal to pass GFP_HIGHMEM in as a GFP flag. Block it in the common
code. Remove the duplicated checks from drivers.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Mostafa Saleh <smostafa@google.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/14-v4-c8663abbb606+3f7-iommu_pages_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/io-pgtable-arm.c

@@ -267,8 +267,6 @@ static void *__arm_lpae_alloc_pages(size_t size, gfp_t gfp,
 	dma_addr_t dma;
 	void *pages;
 
-	VM_BUG_ON((gfp & __GFP_HIGHMEM));
-
 	if (cfg->alloc)
 		pages = cfg->alloc(cookie, size, gfp);
 	else

drivers/iommu/io-pgtable-dart.c

@@ -111,7 +111,6 @@ static void *__dart_alloc_pages(size_t size, gfp_t gfp)
 {
 	int order = get_order(size);
 
-	VM_BUG_ON((gfp & __GFP_HIGHMEM));
 	return iommu_alloc_pages(gfp, order);
 }
 

drivers/iommu/iommu-pages.c

@@ -37,6 +37,10 @@ void *iommu_alloc_pages_node(int nid, gfp_t gfp, unsigned int order)
 	const unsigned long pgcnt = 1UL << order;
 	struct folio *folio;
 
+	/* This uses page_address() on the memory. */
+	if (WARN_ON(gfp & __GFP_HIGHMEM))
+		return NULL;
+
 	/*
 	 * __folio_alloc_node() does not handle NUMA_NO_NODE like
 	 * alloc_pages_node() did.