| Message ID | 20181204082300.95106-1-drinkcat@chromium.org (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | [v3,RFC] iommu/io-pgtable-arm-v7s: Use page_frag to request DMA32 memory | expand |
On Tue, Dec 04, 2018 at 04:23:00PM +0800, Nicolas Boichat wrote: > 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 level 1/2 tables, ensure GFP_DMA32 is used if CONFIG_ZONE_DMA32 > is defined (e.g. on arm64 platforms). > > For level 2 tables (1 KB), we use page_frag to allocate these pages, > as we cannot directly use kmalloc (no slab cache for GFP_DMA32) or > kmem_cache (mm/ code treats GFP_DMA32 as an invalid flag). > > One downside is that we only free the allocated page if all the > 4 fragments (4 IOMMU L2 tables) are freed, but given that we > usually only allocate limited number of IOMMU L2 tables, this > should not have too much impact on memory usage: In the absolute > worst case (4096 L2 page tables, each on their own 4K page), > we would use 16 MB of memory for 4 MB of L2 tables. I think this needs to be documemented in the code. That is move the explanation about into a comment in the code.
On Tue, Dec 04, 2018 at 04:23:00PM +0800, Nicolas Boichat wrote: > 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 level 1/2 tables, ensure GFP_DMA32 is used if CONFIG_ZONE_DMA32 > is defined (e.g. on arm64 platforms). > > For level 2 tables (1 KB), we use page_frag to allocate these pages, > as we cannot directly use kmalloc (no slab cache for GFP_DMA32) or > kmem_cache (mm/ code treats GFP_DMA32 as an invalid flag). > > One downside is that we only free the allocated page if all the > 4 fragments (4 IOMMU L2 tables) are freed, but given that we > usually only allocate limited number of IOMMU L2 tables, this > should not have too much impact on memory usage: In the absolute > worst case (4096 L2 page tables, each on their own 4K page), > we would use 16 MB of memory for 4 MB of L2 tables. > > Also, print an error when the physical address does not fit in > 32-bit, to make debugging easier in the future. > > Fixes: ad67f5a6545f ("arm64: replace ZONE_DMA with ZONE_DMA32") > Signed-off-by: Nicolas Boichat <drinkcat@chromium.org> > --- > > As an alternative to the series [1], which adds support for GFP_DMA32 > to kmem_cache in mm/. IMHO the solution in [1] is cleaner and more > efficient, as it allows freed fragments (L2 tables) to be reused, but > this approach does not require any core change. > > [1] https://patchwork.kernel.org/cover/10677529/, 3 patches > > drivers/iommu/io-pgtable-arm-v7s.c | 32 ++++++++++++++++-------------- > 1 file changed, 17 insertions(+), 15 deletions(-) > > diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c > index 445c3bde04800c..0de6a51eb6755f 100644 > --- a/drivers/iommu/io-pgtable-arm-v7s.c > +++ b/drivers/iommu/io-pgtable-arm-v7s.c > @@ -161,6 +161,12 @@ > > #define ARM_V7S_TCR_PD1 BIT(5) > > +#ifdef CONFIG_ZONE_DMA32 > +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA32 > +#else > +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA > +#endif We may as well include __GFP_ZERO in here too. Anyway, this looks alright to me: Acked-by: Will Deacon <will.deacon@arm.com> But it sounds like you're still on the fence about this patch, so I won't pick it up unless you ask explicitly. Will
diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c index 445c3bde04800c..0de6a51eb6755f 100644 --- a/drivers/iommu/io-pgtable-arm-v7s.c +++ b/drivers/iommu/io-pgtable-arm-v7s.c @@ -161,6 +161,12 @@ #define ARM_V7S_TCR_PD1 BIT(5) +#ifdef CONFIG_ZONE_DMA32 +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA32 +#else +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA +#endif + typedef u32 arm_v7s_iopte; static bool selftest_running; @@ -169,7 +175,7 @@ struct arm_v7s_io_pgtable { struct io_pgtable iop; arm_v7s_iopte *pgd; - struct kmem_cache *l2_tables; + struct page_frag_cache l2_tables; spinlock_t split_lock; }; @@ -198,13 +204,17 @@ static void *__arm_v7s_alloc_table(int lvl, gfp_t gfp, void *table = NULL; if (lvl == 1) - table = (void *)__get_dma_pages(__GFP_ZERO, get_order(size)); + table = (void *)__get_free_pages( + __GFP_ZERO | ARM_V7S_TABLE_GFP_DMA, get_order(size)); else if (lvl == 2) - table = kmem_cache_zalloc(data->l2_tables, gfp | GFP_DMA); + table = page_frag_alloc(&data->l2_tables, size, + gfp | __GFP_ZERO | ARM_V7S_TABLE_GFP_DMA); phys = virt_to_phys(table); - if (phys != (arm_v7s_iopte)phys) + if (phys != (arm_v7s_iopte)phys) { /* Doesn't fit in PTE */ + dev_err(dev, "Page table does not fit in PTE: %pa", &phys); goto out_free; + } if (table && !(cfg->quirks & IO_PGTABLE_QUIRK_NO_DMA)) { dma = dma_map_single(dev, table, size, DMA_TO_DEVICE); if (dma_mapping_error(dev, dma)) @@ -227,7 +237,7 @@ static void *__arm_v7s_alloc_table(int lvl, gfp_t gfp, if (lvl == 1) free_pages((unsigned long)table, get_order(size)); else - kmem_cache_free(data->l2_tables, table); + page_frag_free(table); return NULL; } @@ -244,7 +254,7 @@ static void __arm_v7s_free_table(void *table, int lvl, if (lvl == 1) free_pages((unsigned long)table, get_order(size)); else - kmem_cache_free(data->l2_tables, table); + page_frag_free(table); } static void __arm_v7s_pte_sync(arm_v7s_iopte *ptep, int num_entries, @@ -515,7 +525,6 @@ static void arm_v7s_free_pgtable(struct io_pgtable *iop) __arm_v7s_free_table(iopte_deref(pte, 1), 2, data); } __arm_v7s_free_table(data->pgd, 1, data); - kmem_cache_destroy(data->l2_tables); kfree(data); } @@ -729,17 +738,11 @@ static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg, !(cfg->quirks & IO_PGTABLE_QUIRK_NO_PERMS)) return NULL; - data = kmalloc(sizeof(*data), GFP_KERNEL); + data = kzalloc(sizeof(*data), GFP_KERNEL); if (!data) return NULL; spin_lock_init(&data->split_lock); - data->l2_tables = kmem_cache_create("io-pgtable_armv7s_l2", - ARM_V7S_TABLE_SIZE(2), - ARM_V7S_TABLE_SIZE(2), - SLAB_CACHE_DMA, NULL); - if (!data->l2_tables) - goto out_free_data; data->iop.ops = (struct io_pgtable_ops) { .map = arm_v7s_map, @@ -789,7 +792,6 @@ static struct io_pgtable *arm_v7s_alloc_pgtable(struct io_pgtable_cfg *cfg, return &data->iop; out_free_data: - kmem_cache_destroy(data->l2_tables); kfree(data); return NULL; }
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 level 1/2 tables, ensure GFP_DMA32 is used if CONFIG_ZONE_DMA32 is defined (e.g. on arm64 platforms). For level 2 tables (1 KB), we use page_frag to allocate these pages, as we cannot directly use kmalloc (no slab cache for GFP_DMA32) or kmem_cache (mm/ code treats GFP_DMA32 as an invalid flag). One downside is that we only free the allocated page if all the 4 fragments (4 IOMMU L2 tables) are freed, but given that we usually only allocate limited number of IOMMU L2 tables, this should not have too much impact on memory usage: In the absolute worst case (4096 L2 page tables, each on their own 4K page), we would use 16 MB of memory for 4 MB of L2 tables. Also, print an error when the physical address does not fit in 32-bit, to make debugging easier in the future. Fixes: ad67f5a6545f ("arm64: replace ZONE_DMA with ZONE_DMA32") Signed-off-by: Nicolas Boichat <drinkcat@chromium.org> --- As an alternative to the series [1], which adds support for GFP_DMA32 to kmem_cache in mm/. IMHO the solution in [1] is cleaner and more efficient, as it allows freed fragments (L2 tables) to be reused, but this approach does not require any core change. [1] https://patchwork.kernel.org/cover/10677529/, 3 patches drivers/iommu/io-pgtable-arm-v7s.c | 32 ++++++++++++++++-------------- 1 file changed, 17 insertions(+), 15 deletions(-)