Re: [PATCH v3] misc: sram: Add DMA-BUF Heap exporting of SRAM areas
From: Robin Murphy
Date: Thu Aug 17 2023 - 09:14:57 EST
On 2023-07-13 20:13, Andrew Davis wrote:
This new export type exposes to userspace the SRAM area as a DMA-BUF Heap,
this allows for allocations of DMA-BUFs that can be consumed by various
DMA-BUF supporting devices.
Signed-off-by: Andrew Davis <afd@xxxxxx>
---
Changes from v2:
- Make sram_dma_heap_allocate static (kernel test robot)
- Rebase on v6.5-rc1
drivers/misc/Kconfig | 7 +
drivers/misc/Makefile | 1 +
drivers/misc/sram-dma-heap.c | 245 +++++++++++++++++++++++++++++++++++
drivers/misc/sram.c | 6 +
drivers/misc/sram.h | 16 +++
5 files changed, 275 insertions(+)
create mode 100644 drivers/misc/sram-dma-heap.c
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 75e427f124b28..ee34dfb61605f 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -448,6 +448,13 @@ config SRAM
config SRAM_EXEC
bool
+config SRAM_DMA_HEAP
+ bool "Export on-chip SRAM pools using DMA-Heaps"
+ depends on DMABUF_HEAPS && SRAM
+ help
+ This driver allows the export of on-chip SRAM marked as both pool
+ and exportable to userspace using the DMA-Heaps interface.
+
config DW_XDATA_PCIE
depends on PCI
tristate "Synopsys DesignWare xData PCIe driver"
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index f2a4d1ff65d46..5e7516bfaa8de 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -47,6 +47,7 @@ obj-$(CONFIG_VMWARE_VMCI) += vmw_vmci/
obj-$(CONFIG_LATTICE_ECP3_CONFIG) += lattice-ecp3-config.o
obj-$(CONFIG_SRAM) += sram.o
obj-$(CONFIG_SRAM_EXEC) += sram-exec.o
+obj-$(CONFIG_SRAM_DMA_HEAP) += sram-dma-heap.o
obj-$(CONFIG_GENWQE) += genwqe/
obj-$(CONFIG_ECHO) += echo/
obj-$(CONFIG_CXL_BASE) += cxl/
diff --git a/drivers/misc/sram-dma-heap.c b/drivers/misc/sram-dma-heap.c
new file mode 100644
index 0000000000000..c054c04dff33e
--- /dev/null
+++ b/drivers/misc/sram-dma-heap.c
@@ -0,0 +1,245 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * SRAM DMA-Heap userspace exporter
+ *
+ * Copyright (C) 2019-2022 Texas Instruments Incorporated - https://www.ti.com/
+ * Andrew Davis <afd@xxxxxx>
+ */
+
+#include <linux/dma-mapping.h>
+#include <linux/err.h>
+#include <linux/genalloc.h>
+#include <linux/io.h>
+#include <linux/mm.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-heap.h>
+
+#include "sram.h"
+
+struct sram_dma_heap {
+ struct dma_heap *heap;
+ struct gen_pool *pool;
+};
+
+struct sram_dma_heap_buffer {
+ struct gen_pool *pool;
+ struct list_head attachments;
+ struct mutex attachments_lock;
+ unsigned long len;
+ void *vaddr;
+ phys_addr_t paddr;
+};
+
+struct dma_heap_attachment {
+ struct device *dev;
+ struct sg_table *table;
+ struct list_head list;
+};
+
+static int dma_heap_attach(struct dma_buf *dmabuf,
+ struct dma_buf_attachment *attachment)
+{
+ struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+ struct dma_heap_attachment *a;
+ struct sg_table *table;
+
+ a = kzalloc(sizeof(*a), GFP_KERNEL);
+ if (!a)
+ return -ENOMEM;
+
+ table = kmalloc(sizeof(*table), GFP_KERNEL);
+ if (!table) {
+ kfree(a);
+ return -ENOMEM;
+ }
+ if (sg_alloc_table(table, 1, GFP_KERNEL)) {
+ kfree(table);
+ kfree(a);
+ return -ENOMEM;
+ }
+ sg_set_page(table->sgl, pfn_to_page(PFN_DOWN(buffer->paddr)), buffer->len, 0);
What happens if someone (reasonably) assumes that this struct page
pointer isn't completely made up, and dereferences it?
(That's if pfn_to_page() itself doesn't blow up, which it potentially
might, at least under CONFIG_SPARSEMEM)
I think this needs to be treated as P2PDMA if it's going to have any
hope of working robustly.
+
+ a->table = table;
+ a->dev = attachment->dev;
+ INIT_LIST_HEAD(&a->list);
+
+ attachment->priv = a;
+
+ mutex_lock(&buffer->attachments_lock);
+ list_add(&a->list, &buffer->attachments);
+ mutex_unlock(&buffer->attachments_lock);
+
+ return 0;
+}
+
+static void dma_heap_detatch(struct dma_buf *dmabuf,
+ struct dma_buf_attachment *attachment)
+{
+ struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+ struct dma_heap_attachment *a = attachment->priv;
+
+ mutex_lock(&buffer->attachments_lock);
+ list_del(&a->list);
+ mutex_unlock(&buffer->attachments_lock);
+
+ sg_free_table(a->table);
+ kfree(a->table);
+ kfree(a);
+}
+
+static struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
+ enum dma_data_direction direction)
+{
+ struct dma_heap_attachment *a = attachment->priv;
+ struct sg_table *table = a->table;
+
+ /*
+ * As this heap is backed by uncached SRAM memory we do not need to
+ * perform any sync operations on the buffer before allowing device
+ * domain access. For this reason we use SKIP_CPU_SYNC and also do
+ * not use or provide begin/end_cpu_access() dma-buf functions.
+ */
I bet that works really well with SWIOTLB ;)
Also note that SKIP_CPU_SYNC is only a hint, so the DMA API
implementation is still at liberty to do the fatally dangerous things
you're hoping it won't (e.g. dereferencing sg_virt()...)
Thanks,
Robin.
+ if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents,
+ direction, DMA_ATTR_SKIP_CPU_SYNC))
+ return ERR_PTR(-ENOMEM);
+
+ return table;
+}
+
+static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
+ struct sg_table *table,
+ enum dma_data_direction direction)
+{
+ dma_unmap_sg_attrs(attachment->dev, table->sgl, table->nents,
+ direction, DMA_ATTR_SKIP_CPU_SYNC);
+}
+
+static void dma_heap_dma_buf_release(struct dma_buf *dmabuf)
+{
+ struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+
+ gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
+ kfree(buffer);
+}
+
+static int dma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
+{
+ struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+ int ret;
+
+ /* SRAM mappings are not cached */
+ vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+
+ ret = vm_iomap_memory(vma, buffer->paddr, buffer->len);
+ if (ret)
+ pr_err("Could not map buffer to userspace\n");
+
+ return ret;
+}
+
+static int dma_heap_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
+{
+ struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+
+ iosys_map_set_vaddr(map, buffer->vaddr);
+
+ return 0;
+}
+
+static const struct dma_buf_ops sram_dma_heap_buf_ops = {
+ .attach = dma_heap_attach,
+ .detach = dma_heap_detatch,
+ .map_dma_buf = dma_heap_map_dma_buf,
+ .unmap_dma_buf = dma_heap_unmap_dma_buf,
+ .release = dma_heap_dma_buf_release,
+ .mmap = dma_heap_mmap,
+ .vmap = dma_heap_vmap,
+};
+
+static struct dma_buf *sram_dma_heap_allocate(struct dma_heap *heap,
+ unsigned long len,
+ unsigned long fd_flags,
+ unsigned long heap_flags)
+{
+ struct sram_dma_heap *sram_dma_heap = dma_heap_get_drvdata(heap);
+ struct sram_dma_heap_buffer *buffer;
+
+ DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+ struct dma_buf *dmabuf;
+ int ret = 0;
+
+ buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
+ if (!buffer)
+ return ERR_PTR(-ENOMEM);
+ buffer->pool = sram_dma_heap->pool;
+ INIT_LIST_HEAD(&buffer->attachments);
+ mutex_init(&buffer->attachments_lock);
+ buffer->len = len;
+
+ buffer->vaddr = (void *)gen_pool_alloc(buffer->pool, buffer->len);
+ if (!buffer->vaddr) {
+ ret = -ENOMEM;
+ goto free_buffer;
+ }
+
+ buffer->paddr = gen_pool_virt_to_phys(buffer->pool, (unsigned long)buffer->vaddr);
+ if (buffer->paddr == -1) {
+ ret = -ENOMEM;
+ goto free_pool;
+ }
+
+ /* create the dmabuf */
+ exp_info.exp_name = dma_heap_get_name(heap);
+ exp_info.ops = &sram_dma_heap_buf_ops;
+ exp_info.size = buffer->len;
+ exp_info.flags = fd_flags;
+ exp_info.priv = buffer;
+ dmabuf = dma_buf_export(&exp_info);
+ if (IS_ERR(dmabuf)) {
+ ret = PTR_ERR(dmabuf);
+ goto free_pool;
+ }
+
+ return dmabuf;
+
+free_pool:
+ gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
+free_buffer:
+ kfree(buffer);
+
+ return ERR_PTR(ret);
+}
+
+static struct dma_heap_ops sram_dma_heap_ops = {
+ .allocate = sram_dma_heap_allocate,
+};
+
+int sram_add_dma_heap(struct sram_dev *sram,
+ struct sram_reserve *block,
+ phys_addr_t start,
+ struct sram_partition *part)
+{
+ struct sram_dma_heap *sram_dma_heap;
+ struct dma_heap_export_info exp_info;
+
+ dev_info(sram->dev, "Exporting SRAM Heap '%s'\n", block->label);
+
+ sram_dma_heap = kzalloc(sizeof(*sram_dma_heap), GFP_KERNEL);
+ if (!sram_dma_heap)
+ return -ENOMEM;
+ sram_dma_heap->pool = part->pool;
+
+ exp_info.name = kasprintf(GFP_KERNEL, "sram_%s", block->label);
+ exp_info.ops = &sram_dma_heap_ops;
+ exp_info.priv = sram_dma_heap;
+ sram_dma_heap->heap = dma_heap_add(&exp_info);
+ if (IS_ERR(sram_dma_heap->heap)) {
+ int ret = PTR_ERR(sram_dma_heap->heap);
+ kfree(sram_dma_heap);
+ return ret;
+ }
+
+ return 0;
+}
diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
index 5757adf418b1d..6dd173a2fba8e 100644
--- a/drivers/misc/sram.c
+++ b/drivers/misc/sram.c
@@ -120,6 +120,12 @@ static int sram_add_partition(struct sram_dev *sram, struct sram_reserve *block,
ret = sram_add_pool(sram, block, start, part);
if (ret)
return ret;
+
+ if (block->export) {
+ ret = sram_add_dma_heap(sram, block, start, part);
+ if (ret)
+ return ret;
+ }
}
if (block->export) {
ret = sram_add_export(sram, block, start, part);
diff --git a/drivers/misc/sram.h b/drivers/misc/sram.h
index 397205b8bf6ff..062bdd25fa068 100644
--- a/drivers/misc/sram.h
+++ b/drivers/misc/sram.h
@@ -60,4 +60,20 @@ static inline int sram_add_protect_exec(struct sram_partition *part)
return -ENODEV;
}
#endif /* CONFIG_SRAM_EXEC */
+
+#ifdef CONFIG_SRAM_DMA_HEAP
+int sram_add_dma_heap(struct sram_dev *sram,
+ struct sram_reserve *block,
+ phys_addr_t start,
+ struct sram_partition *part);
+#else
+static inline int sram_add_dma_heap(struct sram_dev *sram,
+ struct sram_reserve *block,
+ phys_addr_t start,
+ struct sram_partition *part)
+{
+ return 0;
+}
+#endif /* CONFIG_SRAM_DMA_HEAP */
+
#endif /* __SRAM_H */