mm: add support for kmem caches in DMA32 zone

Patch series "iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables",
v6.

This is a followup to the discussion in [1], [2].

IOMMUs using ARMv7 short-descriptor format require page tables (level 1
and 2) to be allocated within the first 4GB of RAM, even on 64-bit
systems.

For L1 tables that are bigger than a page, we can just use
__get_free_pages with GFP_DMA32 (on arm64 systems only, arm would still
use GFP_DMA).

For L2 tables that only take 1KB, it would be a waste to allocate a full
page, so we considered 3 approaches:
 1. This series, adding support for GFP_DMA32 slab caches.
 2. genalloc, which requires pre-allocating the maximum number of L2 page
    tables (4096, so 4MB of memory).
 3. page_frag, which is not very memory-efficient as it is unable to reuse
    freed fragments until the whole page is freed. [3]

This series is the most memory-efficient approach.

stable@ note:
  We confirmed that this is a regression, and IOMMU errors happen on 4.19
  and linux-next/master on MT8173 (elm, Acer Chromebook R13). The issue
  most likely starts from commit ad67f5a654 ("arm64: replace ZONE_DMA
  with ZONE_DMA32"), i.e. 4.15, and presumably breaks a number of Mediatek
  platforms (and maybe others?).

[1] https://lists.linuxfoundation.org/pipermail/iommu/2018-November/030876.html
[2] https://lists.linuxfoundation.org/pipermail/iommu/2018-December/031696.html
[3] https://patchwork.codeaurora.org/patch/671639/

This patch (of 3):

IOMMUs using ARMv7 short-descriptor format require page tables to be
allocated within the first 4GB of RAM, even on 64-bit systems.  On arm64,
this is done by passing GFP_DMA32 flag to memory allocation functions.

For IOMMU L2 tables that only take 1KB, it would be a waste to allocate
a full page using get_free_pages, so we considered 3 approaches:
 1. This patch, adding support for GFP_DMA32 slab caches.
 2. genalloc, which requires pre-allocating the maximum number of L2
    page tables (4096, so 4MB of memory).
 3. page_frag, which is not very memory-efficient as it is unable
    to reuse freed fragments until the whole page is freed.

This change makes it possible to create a custom cache in DMA32 zone using
kmem_cache_create, then allocate memory using kmem_cache_alloc.

We do not create a DMA32 kmalloc cache array, as there are currently no
users of kmalloc(..., GFP_DMA32).  These calls will continue to trigger a
warning, as we keep GFP_DMA32 in GFP_SLAB_BUG_MASK.

This implies that calls to kmem_cache_*alloc on a SLAB_CACHE_DMA32
kmem_cache must _not_ use GFP_DMA32 (it is anyway redundant and
unnecessary).

Link: http://lkml.kernel.org/r/20181210011504.122604-2-drinkcat@chromium.org
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Sasha Levin <Alexander.Levin@microsoft.com>
Cc: Huaisheng Ye <yehs1@lenovo.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Yong Wu <yong.wu@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Tomasz Figa <tfiga@google.com>
Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/slab.h

@@ -32,6 +32,8 @@
 #define SLAB_HWCACHE_ALIGN	((slab_flags_t __force)0x00002000U)
 /* Use GFP_DMA memory */
 #define SLAB_CACHE_DMA		((slab_flags_t __force)0x00004000U)
+/* Use GFP_DMA32 memory */
+#define SLAB_CACHE_DMA32	((slab_flags_t __force)0x00008000U)
 /* DEBUG: Store the last owner for bug hunting */
 #define SLAB_STORE_USER		((slab_flags_t __force)0x00010000U)
 /* Panic if kmem_cache_create() fails */

mm/slab.c

@@ -2115,6 +2115,8 @@ done:
 	cachep->allocflags = __GFP_COMP;
 	if (flags & SLAB_CACHE_DMA)
 		cachep->allocflags |= GFP_DMA;
+	if (flags & SLAB_CACHE_DMA32)
+		cachep->allocflags |= GFP_DMA32;
 	if (flags & SLAB_RECLAIM_ACCOUNT)
 		cachep->allocflags |= __GFP_RECLAIMABLE;
 	cachep->size = size;

mm/slab.h

@@ -127,7 +127,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
 
 
 /* Legal flag mask for kmem_cache_create(), for various configurations */
-#define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | SLAB_PANIC | \
+#define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | \
+			 SLAB_CACHE_DMA32 | SLAB_PANIC | \
 			 SLAB_TYPESAFE_BY_RCU | SLAB_DEBUG_OBJECTS )
 
 #if defined(CONFIG_DEBUG_SLAB)

mm/slab_common.c

@@ -53,7 +53,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
 		SLAB_FAILSLAB | SLAB_KASAN)
 
 #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
-			 SLAB_ACCOUNT)
+			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT)
 
 /*
  * Merge control. If this is set then no merging of slab caches will occur.

mm/slub.c

@@ -3589,6 +3589,9 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
 	if (s->flags & SLAB_CACHE_DMA)
 		s->allocflags |= GFP_DMA;
 
+	if (s->flags & SLAB_CACHE_DMA32)
+		s->allocflags |= GFP_DMA32;
+
 	if (s->flags & SLAB_RECLAIM_ACCOUNT)
 		s->allocflags |= __GFP_RECLAIMABLE;
 
@@ -5679,6 +5682,8 @@ static char *create_unique_id(struct kmem_cache *s)
 	 */
 	if (s->flags & SLAB_CACHE_DMA)
 		*p++ = 'd';
+	if (s->flags & SLAB_CACHE_DMA32)
+		*p++ = 'D';
 	if (s->flags & SLAB_RECLAIM_ACCOUNT)
 		*p++ = 'a';
 	if (s->flags & SLAB_CONSISTENCY_CHECKS)