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SubjectRe: [PATCH v2 07/12] drivers/soc: xdma: Add user interface
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On 12/10/19 9:48 PM, Andrew Jeffery wrote:
>
> 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.


Sure.


>
>> + }
>> + } 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?


That's correct, that is the intention. In case the transfer hangs,
another client needs to be able to reset and clear up a blocking transfer.


>
>> +
>> + 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.


Good point.


>
>> +
>> + 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?


Right, better wait for completion. There's no way to cancel a transfer.


>
>> +
>> + 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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