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SubjectRe: [PATCH v2 07/12] drivers/soc: xdma: Add user interface


On Fri, 6 Dec 2019, at 03:45, Eddie James wrote:
> This commits adds a miscdevice to provide a user interface to the XDMA
> engine. The interface provides the write operation to start DMA
> operations. The DMA parameters are passed as the data to the write call.
> The actual data to transfer is NOT passed through write. Note that both
> directions of DMA operation are accomplished through the write command;
> BMC to host and host to BMC.
>
> The XDMA engine is restricted to only accessing the reserved memory
> space on the AST2500, typically used by the VGA. For this reason, the
> VGA memory space is pooled and allocated with genalloc. Users calling
> mmap allocate pages from this pool for their usage. The space allocated
> by a client will be the space used in the DMA operation. For an
> "upstream" (BMC to host) operation, the data in the client's area will
> be transferred to the host. For a "downstream" (host to BMC) operation,
> the host data will be placed in the client's memory area.

Given the comments on earlier patches we should reconsider descriptions
of the VGA area in this paragraph.

>
> Poll is also provided in order to determine when the DMA operation is
> complete for non-blocking IO.
>
> Signed-off-by: Eddie James <eajames@linux.ibm.com>
> ---
> Changes since v1:
> - Add file_lock comment
> - Bring user reset up to date with new reset method
>
> drivers/soc/aspeed/aspeed-xdma.c | 224 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 224 insertions(+)
>
> diff --git a/drivers/soc/aspeed/aspeed-xdma.c b/drivers/soc/aspeed/aspeed-xdma.c
> index a9b3eeb..d4b96a7 100644
> --- a/drivers/soc/aspeed/aspeed-xdma.c
> +++ b/drivers/soc/aspeed/aspeed-xdma.c
> @@ -13,6 +13,7 @@
> #include <linux/io.h>
> #include <linux/jiffies.h>
> #include <linux/mfd/syscon.h>
> +#include <linux/miscdevice.h>
> #include <linux/module.h>
> #include <linux/mutex.h>
> #include <linux/of_device.h>
> @@ -206,6 +207,8 @@ struct aspeed_xdma {
> struct clk *clock;
> struct reset_control *reset;
>
> + /* file_lock serializes reads of current_client */
> + struct mutex file_lock;
> struct aspeed_xdma_client *current_client;
>
> /* start_lock protects cmd_idx, cmdq, and the state of the engine */
> @@ -227,6 +230,8 @@ struct aspeed_xdma {
> dma_addr_t cmdq_vga_phys;
> void *cmdq_vga_virt;
> struct gen_pool *vga_pool;
> +
> + struct miscdevice misc;
> };
>
> struct aspeed_xdma_client {
> @@ -517,6 +522,207 @@ static irqreturn_t aspeed_xdma_pcie_irq(int irq,
> void *arg)
> return IRQ_HANDLED;
> }
>
> +static ssize_t aspeed_xdma_write(struct file *file, const char __user *buf,
> + size_t len, loff_t *offset)
> +{
> + int rc;
> + struct aspeed_xdma_op op;
> + struct aspeed_xdma_client *client = file->private_data;
> + struct aspeed_xdma *ctx = client->ctx;
> + u32 offs = client->phys ? (client->phys - ctx->vga_phys) :
> + XDMA_CMDQ_SIZE;
> +
> + if (len != sizeof(op))
> + return -EINVAL;
> +
> + rc = copy_from_user(&op, buf, len);
> + if (rc)
> + return rc;
> +
> + if (op.direction == ASPEED_XDMA_DIRECTION_RESET) {
> + unsigned long flags;
> +
> + spin_lock_irqsave(&ctx->reset_lock, flags);
> + if (ctx->in_reset) {
> + spin_unlock_irqrestore(&ctx->reset_lock, flags);
> + return len;
> + }
> +
> + ctx->in_reset = true;
> + spin_unlock_irqrestore(&ctx->reset_lock, flags);
> +
> + mutex_lock(&ctx->start_lock);
> +
> + aspeed_xdma_reset(ctx);
> +
> + mutex_unlock(&ctx->start_lock);
> +
> + return len;
> + } else if (op.direction > ASPEED_XDMA_DIRECTION_RESET) {
> + return -EINVAL;
> + }
> +
> + if (op.len > ctx->vga_size - offs)
> + return -EINVAL;

I'm wondering if we can rearrange the code to move the sanity checks to the
top of the function, so this and the `op.direction >
ASPEED_XDMA_DIRECTION_RESET` case.

The check above should fail for the reset case as well, I expect op.len should
be set to zero in that case. But I still think that jamming the reset command
into a "direction" concept feels broken, so as mentioned on an earlier patch
I'd prefer we move that distraction out to a separate patch.

> +
> + if (file->f_flags & O_NONBLOCK) {
> + if (!mutex_trylock(&ctx->file_lock))
> + return -EAGAIN;
> +
> + if (ctx->current_client) {
> + mutex_unlock(&ctx->file_lock);
> + return -EAGAIN;

I think EBUSY is better here.

> + }
> + } else {
> + mutex_lock(&ctx->file_lock);
> +
> + rc = wait_event_interruptible(ctx->wait, !ctx->current_client);
> + if (rc) {
> + mutex_unlock(&ctx->file_lock);
> + return -EINTR;
> + }
> + }
> +
> + aspeed_xdma_start(ctx, &op, ctx->vga_phys + offs, client);
> +
> + mutex_unlock(&ctx->file_lock);

You've used file_lock here to protect aspeed_xdma_start() but start_lock
above to protect aspeed_xdma_reset(), so it seems one client can disrupt
another by resetting the engine while a DMA is in progress?

> +
> + if (!(file->f_flags & O_NONBLOCK)) {
> + rc = wait_event_interruptible(ctx->wait, !client->in_progress);
> + if (rc)
> + return -EINTR;
> +
> + if (client->error)
> + return -EIO;
> + }
> +
> + return len;
> +}
> +
> +static __poll_t aspeed_xdma_poll(struct file *file,
> + struct poll_table_struct *wait)
> +{
> + __poll_t mask = 0;
> + __poll_t req = poll_requested_events(wait);
> + struct aspeed_xdma_client *client = file->private_data;
> + struct aspeed_xdma *ctx = client->ctx;
> +
> + if (req & (EPOLLIN | EPOLLRDNORM)) {
> + if (client->in_progress)
> + poll_wait(file, &ctx->wait, wait);
> +
> + if (!client->in_progress) {
> + if (client->error)
> + mask |= EPOLLERR;
> + else
> + mask |= EPOLLIN | EPOLLRDNORM;
> + }
> + }
> +
> + if (req & (EPOLLOUT | EPOLLWRNORM)) {
> + if (ctx->current_client)
> + poll_wait(file, &ctx->wait, wait);
> +
> + if (!ctx->current_client)
> + mask |= EPOLLOUT | EPOLLWRNORM;
> + }
> +
> + return mask;
> +}
> +
> +static void aspeed_xdma_vma_close(struct vm_area_struct *vma)
> +{
> + struct aspeed_xdma_client *client = vma->vm_private_data;
> +
> + gen_pool_free(client->ctx->vga_pool, (unsigned long)client->virt,
> + client->size);

What assurance do we have that a DMA isn't in progress? With non-blocking
IO we could easily start one then close the file descriptor, which would cause
havoc if the physical range is reused by a subsequent mapping.

> +
> + client->virt = NULL;
> + client->phys = 0;
> + client->size = 0;
> +}
> +
> +static const struct vm_operations_struct aspeed_xdma_vm_ops = {
> + .close = aspeed_xdma_vma_close,
> +};
> +
> +static int aspeed_xdma_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + int rc;
> + struct aspeed_xdma_client *client = file->private_data;
> + struct aspeed_xdma *ctx = client->ctx;
> +
> + /* restrict file to one mapping */
> + if (client->size)
> + return -ENOMEM;
> +
> + client->size = vma->vm_end - vma->vm_start;
> + client->virt = gen_pool_dma_alloc(ctx->vga_pool, client->size,
> + &client->phys);
> + if (!client->virt) {
> + client->phys = 0;
> + client->size = 0;
> + return -ENOMEM;
> + }
> +
> + vma->vm_pgoff = (client->phys - ctx->vga_phys) >> PAGE_SHIFT;
> + vma->vm_ops = &aspeed_xdma_vm_ops;
> + vma->vm_private_data = client;
> + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> +
> + rc = io_remap_pfn_range(vma, vma->vm_start, client->phys >> PAGE_SHIFT,
> + client->size, vma->vm_page_prot);
> + if (rc) {
> + gen_pool_free(ctx->vga_pool, (unsigned long)client->virt,
> + client->size);
> +
> + client->virt = NULL;
> + client->phys = 0;
> + client->size = 0;
> + return rc;
> + }
> +
> + dev_dbg(ctx->dev, "mmap: v[%08lx] to p[%08x], s[%08x]\n",
> + vma->vm_start, (u32)client->phys, client->size);
> +
> + return 0;
> +}
> +
> +static int aspeed_xdma_open(struct inode *inode, struct file *file)
> +{
> + struct miscdevice *misc = file->private_data;
> + struct aspeed_xdma *ctx = container_of(misc, struct aspeed_xdma, misc);
> + struct aspeed_xdma_client *client = kzalloc(sizeof(*client),
> + GFP_KERNEL);
> +
> + if (!client)
> + return -ENOMEM;
> +
> + client->ctx = ctx;
> + file->private_data = client;
> + return 0;
> +}
> +
> +static int aspeed_xdma_release(struct inode *inode, struct file *file)
> +{
> + struct aspeed_xdma_client *client = file->private_data;
> +
> + if (client->ctx->current_client == client)
> + client->ctx->current_client = NULL;

Shouldn't we also cancel the DMA op? This seems like a DoS risk: set up
a non-blocking, large downstream transfer then close the client. Also risks
scribbling on memory we no-longer own given we don't cancel/wait for
completion in vm close callback?

> +
> + kfree(client);
> + return 0;
> +}
> +
> +static const struct file_operations aspeed_xdma_fops = {
> + .owner = THIS_MODULE,
> + .write = aspeed_xdma_write,
> + .poll = aspeed_xdma_poll,
> + .mmap = aspeed_xdma_mmap,
> + .open = aspeed_xdma_open,
> + .release = aspeed_xdma_release,
> +};
> +
> static int aspeed_xdma_probe(struct platform_device *pdev)
> {
> int irq;
> @@ -539,6 +745,7 @@ static int aspeed_xdma_probe(struct platform_device *pdev)
> ctx->chip = md;
> ctx->dev = dev;
> platform_set_drvdata(pdev, ctx);
> + mutex_init(&ctx->file_lock);
> mutex_init(&ctx->start_lock);
> INIT_WORK(&ctx->reset_work, aspeed_xdma_reset_work);
> spin_lock_init(&ctx->reset_lock);
> @@ -678,6 +885,22 @@ static int aspeed_xdma_probe(struct platform_device *pdev)
>
> aspeed_xdma_init_eng(ctx);
>
> + ctx->misc.minor = MISC_DYNAMIC_MINOR;
> + ctx->misc.fops = &aspeed_xdma_fops;
> + ctx->misc.name = "aspeed-xdma";
> + ctx->misc.parent = dev;
> + rc = misc_register(&ctx->misc);
> + if (rc) {
> + dev_err(dev, "Failed to register xdma miscdevice.\n");
> +
> + gen_pool_free(ctx->vga_pool, (unsigned long)ctx->cmdq_vga_virt,
> + XDMA_CMDQ_SIZE);
> +
> + reset_control_assert(ctx->reset);
> + clk_disable_unprepare(ctx->clock);
> + return rc;
> + }
> +
> /*
> * This interrupt could fire immediately so only request it once the
> * engine and driver are initialized.
> @@ -699,6 +922,7 @@ static int aspeed_xdma_remove(struct platform_device *pdev)
> {
> struct aspeed_xdma *ctx = platform_get_drvdata(pdev);
>
> + misc_deregister(&ctx->misc);
> gen_pool_free(ctx->vga_pool, (unsigned long)ctx->cmdq_vga_virt,
> XDMA_CMDQ_SIZE);
>
> --
> 1.8.3.1
>
>

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