Re: [PATCH 2/2] nvme-apple: Prevent tag collision across queues even if tag space is shared

[David Laight <david.laight.linux@gmail.com>]

On Sat, 06 Jun 2026 21:25:26 +0800
Nick Chan <towinchenmi@gmail.com> wrote:

> From: Yuriy Havrylyuk <yhavry@gmail.com>
> 
> Apple NVMe controllers require tags of pending commands to not be shared
> across admin and IO queues. However, on Apple A11 without linear SQ, it is
> not possible for either queue to skip over some tags and must go from 0 to
> the configured maximum before wrapping around.
> 
> If a pending command tag is duplicated across queues, the firmware
> crashes with: "duplicate tag error for tag N", with N being the tag.
> 
> Instead of partitioning the tag space, which is not possible without
> linear SQ, prevent tag collisions by keeping track of which tags are
> currently in-flight across either queues, and return BLK_STS_RESOURCE to
> temporaily block command submission when a collision would have occurred.

I look at using the atomic64_xxx() functions rather than the bitmask ones.
The for_each_bit_set() loop is then an atmomic64_andnot() call.

-- David


> 
> Cc: stable@vger.kernel.org
> Fixes: 04d8ecf37b5e ("nvme: apple: Add Apple A11 support")
> Signed-off-by: Yuriy Havrylyuk <yhavry@gmail.com>
> Co-developed-by: Nick Chan <towinchenmi@gmail.com>
> Signed-off-by: Nick Chan <towinchenmi@gmail.com>
> ---
>  drivers/nvme/host/apple.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 65 insertions(+)
> 
> diff --git a/drivers/nvme/host/apple.c b/drivers/nvme/host/apple.c
> index c1115e27a0d6..6354edf27225 100644
> --- a/drivers/nvme/host/apple.c
> +++ b/drivers/nvme/host/apple.c
> @@ -203,6 +203,20 @@ struct apple_nvme {
>  
>  	int irq;
>  	spinlock_t lock;
> +
> +	/*
> +	 * Tags of pending commands must be unique across both Admin and IO
> +	 * queue. However, on T8015, unlike T8103, without linear submission
> +	 * queues, it is not possible for the either queue to skip some tags,
> +	 * and both queues must go from 0 to their respective configured
> +	 * maximum.
> +	 *
> +	 * Instead of reserving some tags for the admin queue, use a bitfield
> +	 * to keep track of pending commands on either queue, and temporaily
> +	 * block command submission by returning BLK_STS_RESOURCE until the
> +	 * tag is freed on the other queue.
> +	 */
> +	unsigned long t8015_active_tags;
>  };
>  
>  static_assert(sizeof(struct nvme_command) == 64);
> @@ -290,6 +304,28 @@ static void apple_nvmmu_inval(struct apple_nvme_queue *q, unsigned int tag)
>  				     "NVMMU TCB invalidation failed\n");
>  }
>  
> +static bool apple_nvme_reserve_tag_t8015(struct apple_nvme *anv,
> +					 struct nvme_command *cmd)
> +{
> +	u16 tag = nvme_tag_from_cid(cmd->common.command_id);
> +
> +	if (WARN_ON_ONCE(tag >= BITS_PER_LONG))
> +		return false;
> +
> +	return !test_and_set_bit(tag, &anv->t8015_active_tags);
> +}
> +
> +static void apple_nvme_release_tag_t8015(struct apple_nvme *anv,
> +					 __u16 command_id)
> +{
> +	u16 tag = nvme_tag_from_cid(command_id);
> +
> +	if (WARN_ON_ONCE(tag >= BITS_PER_LONG))
> +		return;
> +
> +	clear_bit(tag, &anv->t8015_active_tags);
> +}
> +
>  static void apple_nvme_submit_cmd_t8015(struct apple_nvme_queue *q,
>  				  struct nvme_command *cmd)
>  {
> @@ -652,6 +688,8 @@ static inline void apple_nvme_update_cq_head(struct apple_nvme_queue *q)
>  static bool apple_nvme_poll_cq(struct apple_nvme_queue *q,
>  			       struct io_comp_batch *iob)
>  {
> +	struct apple_nvme *anv = queue_to_apple_nvme(q);
> +	unsigned long completed_tags = 0;
>  	bool found = false;
>  
>  	while (apple_nvme_cqe_pending(q)) {
> @@ -664,11 +702,26 @@ static bool apple_nvme_poll_cq(struct apple_nvme_queue *q,
>  		dma_rmb();
>  		apple_nvme_handle_cqe(q, iob, q->cq_head);
>  		apple_nvme_update_cq_head(q);
> +
> +		if (!anv->hw->has_lsq_nvmmu) {
> +			struct nvme_completion *cqe = &q->cqes[q->cq_head];
> +			u16 tag = nvme_tag_from_cid(READ_ONCE(cqe->command_id));
> +
> +			if (!WARN_ON_ONCE(tag >= BITS_PER_LONG))
> +				__set_bit(tag, &completed_tags);
> +		}
>  	}
>  
>  	if (found)
>  		writel(q->cq_head, q->cq_db);
>  
> +	if (!anv->hw->has_lsq_nvmmu && completed_tags) {
> +		unsigned long tag_bit;
> +
> +		for_each_set_bit(tag_bit, &completed_tags, BITS_PER_LONG)
> +			clear_bit(tag_bit, &anv->t8015_active_tags);
> +	}
> +
>  	return found;
>  }
>  
> @@ -790,6 +843,12 @@ static blk_status_t apple_nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
>  	if (ret)
>  		return ret;
>  
> +	if (!anv->hw->has_lsq_nvmmu &&
> +	    !apple_nvme_reserve_tag_t8015(anv, cmnd)) {
> +		ret = BLK_STS_RESOURCE;
> +		goto out_free_cmd;
> +	}
> +
>  	if (blk_rq_nr_phys_segments(req)) {
>  		ret = apple_nvme_map_data(anv, req, cmnd);
>  		if (ret)
> @@ -806,6 +865,9 @@ static blk_status_t apple_nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
>  	return BLK_STS_OK;
>  
>  out_free_cmd:
> +	if (!anv->hw->has_lsq_nvmmu)
> +		apple_nvme_release_tag_t8015(anv, cmnd->common.command_id);
> +
>  	nvme_cleanup_cmd(req);
>  	return ret;
>  }
> @@ -1165,6 +1227,9 @@ static void apple_nvme_reset_work(struct work_struct *work)
>  	if (ret)
>  		goto out;
>  
> +	if (!anv->hw->has_lsq_nvmmu)
> +		WRITE_ONCE(anv->t8015_active_tags, 0);
> +
>  	dev_dbg(anv->dev, "Starting admin queue");
>  	apple_nvme_init_queue(&anv->adminq);
>  	nvme_unquiesce_admin_queue(&anv->ctrl);
>