From: Nicolas Boichat drinkcat@chromium.org Subject: 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 ad67f5a6545f ("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 ---

include/linux/slab.h | 2 ++ mm/slab.c | 2 ++ mm/slab.h | 3 ++- mm/slab_common.c | 2 +- mm/slub.c | 5 +++++ 5 files changed, 12 insertions(+), 2 deletions(-)

--- a/include/linux/slab.h~mm-add-support-for-kmem-caches-in-dma32-zone +++ a/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 */ --- a/mm/slab.c~mm-add-support-for-kmem-caches-in-dma32-zone +++ a/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; --- a/mm/slab_common.c~mm-add-support-for-kmem-caches-in-dma32-zone +++ a/mm/slab_common.c @@ -53,7 +53,7 @@ static DECLARE_WORK(slab_caches_to_rcu_d 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. --- a/mm/slab.h~mm-add-support-for-kmem-caches-in-dma32-zone +++ a/mm/slab.h @@ -127,7 +127,8 @@ static inline slab_flags_t kmem_cache_fl

/* 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) --- a/mm/slub.c~mm-add-support-for-kmem-caches-in-dma32-zone +++ a/mm/slub.c @@ -3589,6 +3589,9 @@ static int calculate_sizes(struct kmem_c 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 kme */ 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) _