mm: remove a pointless CONFIG_ZONE_DEVICE check in memremap_pages

Patch series "start sorting out the ZONE_DEVICE refcount mess", v2.

This series removes the offset by one refcount for ZONE_DEVICE pages that
are freed back to the driver owning them, which is just device private
ones for now, but also the planned device coherent pages and the ehanced
p2p ones pending.

It does not address the fsdax pages yet, which will be attacked in a
follow on series.

This patch (of 27):

memremap.c is only built when CONFIG_ZONE_DEVICE is set, so remove
the superflous extra check.

Link: https://lkml.kernel.org/r/20220210072828.2930359-1-hch@lst.de
Link: https://lkml.kernel.org/r/20220210072828.2930359-2-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian Knig <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

mm/memremap.c

@@ -328,8 +328,7 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 		}
 		break;
 	case MEMORY_DEVICE_FS_DAX:
-		if (!IS_ENABLED(CONFIG_ZONE_DEVICE) ||
-		    IS_ENABLED(CONFIG_FS_DAX_LIMITED)) {
+		if (IS_ENABLED(CONFIG_FS_DAX_LIMITED)) {
 			WARN(1, "File system DAX not supported\n");
 			return ERR_PTR(-EINVAL);
 		}