Date:   Fri, 19 Jul 2019 14:49:15 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Damien Le Moal <Damien.LeMoal@....com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Paul Pawlowski <paul@...rm.io>, Jens Axboe <axboe@...com>,
        Minwoo Im <minwoo.im.dev@...il.com>,
        Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] nvme-pci: Support shared tags across queues for
 Apple 2018 controllers

On Fri, 2019-07-19 at 04:43 +0000, Damien Le Moal wrote:
> On 2019/07/19 13:37, Benjamin Herrenschmidt wrote:
> > Another issue with the Apple T2 based 2018 controllers seem to be
> > that they blow up (and shut the machine down) if there's a tag
> > collision between the IO queue and the Admin queue.
> > 
> > My suspicion is that they use our tags for their internal tracking
> > and don't mix them with the queue id. They also seem to not like
> > when tags go beyond the IO queue depth, ie 128 tags.
> > 
> > This adds a quirk that offsets all the tags in the IO queue by 32
> > to avoid those collisions. It also limits the number of IO queues
> > to 1 since the code wouldn't otherwise make sense (the device
> > supports only one queue anyway but better safe than sorry) and
> > reduces the size of the IO queue
> 
> What about keeping the IO queue QD at 128, but marking the first 32 tags as
> "allocated" when the device is initialized ? This way, these tags numbers are
> never used for regular IOs and you can avoid the entire tag +/- offset dance at
> runtime. The admin queue uses tags 0-31 and the IO queue uses tags 32-127. No ?

I suppose that would work and be simpler. I honestly don't know much
about the block layer and tag allocation so I stayed away from it :-)

I'll dig, but a hint would be welcome :)

Cheers,
Ben.

> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> > ---
> > 
> > Note: One thing I noticed is how we have nvme_completion as volatile.
> > 
> > I don't think we really need that, it's forcing the compiler to constantly
> > reload things which makes no sense once we have established that an
> > entry is valid.
> > 
> > And since we have a data & control dependency from nvme_cqe_pending(),
> > we know that reading the CQE is going to depend on it being valid. I
> > don't really see what volatile is buying us here other than cargo culting.
> > 
> > Cheers,
> > Ben.
> > 
> >  drivers/nvme/host/nvme.h |  5 ++++
> >  drivers/nvme/host/pci.c  | 52 +++++++++++++++++++++++++++++++++-------
> >  2 files changed, 49 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> > index ced0e0a7e039..7c6de398de7d 100644
> > --- a/drivers/nvme/host/nvme.h
> > +++ b/drivers/nvme/host/nvme.h
> > @@ -102,6 +102,11 @@ enum nvme_quirks {
> >  	 * Use non-standard 128 bytes SQEs.
> >  	 */
> >  	NVME_QUIRK_128_BYTES_SQES		= (1 << 11),
> > +
> > +	/*
> > +	 * Prevent tag overlap between queues
> > +	 */
> > +	NVME_QUIRK_SHARED_TAGS			= (1 << 12),
> >  };
> >  
> >  /*
> > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> > index 7088971d4c42..c38e946ad8ca 100644
> > --- a/drivers/nvme/host/pci.c
> > +++ b/drivers/nvme/host/pci.c
> > @@ -178,6 +178,7 @@ struct nvme_queue {
> >  	u16 cq_head;
> >  	u16 last_cq_head;
> >  	u16 qid;
> > +	u16 tag_offset;
> >  	u8 cq_phase;
> >  	u8 sqes;
> >  	unsigned long flags;
> > @@ -490,6 +491,7 @@ static void nvme_submit_cmd(struct nvme_queue *nvmeq, struct nvme_command *cmd,
> >  			    bool write_sq)
> >  {
> >  	spin_lock(&nvmeq->sq_lock);
> > +	cmd->common.command_id += nvmeq->tag_offset;
> >  	memcpy(nvmeq->sq_cmds + (nvmeq->sq_tail << nvmeq->sqes),
> >  	       cmd, sizeof(*cmd));
> >  	if (++nvmeq->sq_tail == nvmeq->q_depth)
> > @@ -951,9 +953,10 @@ static inline void nvme_ring_cq_doorbell(struct nvme_queue *nvmeq)
> >  static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
> >  {
> >  	volatile struct nvme_completion *cqe = &nvmeq->cqes[idx];
> > +	u16 ctag = cqe->command_id - nvmeq->tag_offset;
> >  	struct request *req;
> >  
> > -	if (unlikely(cqe->command_id >= nvmeq->q_depth)) {
> > +	if (unlikely(ctag >= nvmeq->q_depth)) {
> >  		dev_warn(nvmeq->dev->ctrl.device,
> >  			"invalid id %d completed on queue %d\n",
> >  			cqe->command_id, le16_to_cpu(cqe->sq_id));
> > @@ -966,14 +969,13 @@ static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
> >  	 * aborts.  We don't even bother to allocate a struct request
> >  	 * for them but rather special case them here.
> >  	 */
> > -	if (unlikely(nvmeq->qid == 0 &&
> > -			cqe->command_id >= NVME_AQ_BLK_MQ_DEPTH)) {
> > +	if (unlikely(nvmeq->qid == 0 && ctag >= NVME_AQ_BLK_MQ_DEPTH)) {
> >  		nvme_complete_async_event(&nvmeq->dev->ctrl,
> >  				cqe->status, &cqe->result);
> >  		return;
> >  	}
> >  
> > -	req = blk_mq_tag_to_rq(*nvmeq->tags, cqe->command_id);
> > +	req = blk_mq_tag_to_rq(*nvmeq->tags, ctag);
> >  	trace_nvme_sq(req, cqe->sq_head, nvmeq->sq_tail);
> >  	nvme_end_request(req, cqe->status, cqe->result);
> >  }
> > @@ -1004,7 +1006,10 @@ static inline int nvme_process_cq(struct nvme_queue *nvmeq, u16 *start,
> >  
> >  	*start = nvmeq->cq_head;
> >  	while (nvme_cqe_pending(nvmeq)) {
> > -		if (tag == -1U || nvmeq->cqes[nvmeq->cq_head].command_id == tag)
> > +		u16 ctag = nvmeq->cqes[nvmeq->cq_head].command_id;
> > +
> > +		ctag -= nvmeq->tag_offset;
> > +		if (tag == -1U || ctag == tag)
> >  			found++;
> >  		nvme_update_cq_head(nvmeq);
> >  	}
> > @@ -1487,6 +1492,10 @@ static int nvme_alloc_queue(struct nvme_dev *dev, int qid, int depth)
> >  	nvmeq->qid = qid;
> >  	dev->ctrl.queue_count++;
> >  
> > +	if (qid && (dev->ctrl.quirks & NVME_QUIRK_SHARED_TAGS))
> > +		nvmeq->tag_offset = NVME_AQ_DEPTH;
> > +	else
> > +		nvmeq->tag_offset = 0;
> >  	return 0;
> >  
> >   free_cqdma:
> > @@ -2106,6 +2115,14 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
> >  	unsigned long size;
> >  
> >  	nr_io_queues = max_io_queues();
> > +
> > +	/*
> > +	 * If tags are shared with admin queue (Apple bug), then
> > +	 * make sure we only use one queue.
> > +	 */
> > +	if (dev->ctrl.quirks & NVME_QUIRK_SHARED_TAGS)
> > +		nr_io_queues = 1;
> > +
> >  	result = nvme_set_queue_count(&dev->ctrl, &nr_io_queues);
> >  	if (result < 0)
> >  		return result;
> > @@ -2300,6 +2317,7 @@ static int nvme_pci_enable(struct nvme_dev *dev)
> >  {
> >  	int result = -ENOMEM;
> >  	struct pci_dev *pdev = to_pci_dev(dev->dev);
> > +	unsigned int mqes;
> >  
> >  	if (pci_enable_device_mem(pdev))
> >  		return result;
> > @@ -2325,8 +2343,8 @@ static int nvme_pci_enable(struct nvme_dev *dev)
> >  
> >  	dev->ctrl.cap = lo_hi_readq(dev->bar + NVME_REG_CAP);
> >  
> > -	dev->q_depth = min_t(int, NVME_CAP_MQES(dev->ctrl.cap) + 1,
> > -				io_queue_depth);
> > +	mqes = NVME_CAP_MQES(dev->ctrl.cap);
> > +	dev->q_depth = min_t(int, mqes + 1, io_queue_depth);
> >  	dev->db_stride = 1 << NVME_CAP_STRIDE(dev->ctrl.cap);
> >  	dev->dbs = dev->bar + 4096;
> >  
> > @@ -2340,6 +2358,23 @@ static int nvme_pci_enable(struct nvme_dev *dev)
> >  	else
> >  		dev->io_sqes = NVME_NVM_IOSQES;
> >  
> > +	/*
> > +	 * Another Apple one: If we're going to offset the IO queue tags,
> > +	 * we still want to make sure they are no bigger than MQES,
> > +	 * it *looks* like otherwise, bad things happen (I suspect some
> > +	 * of the tag tracking in that device is limited).
> > +	 */
> > +	if (dev->ctrl.quirks & NVME_QUIRK_SHARED_TAGS) {
> > +		if (mqes <= NVME_AQ_DEPTH) {
> > +			dev_err(dev->ctrl.device, "Apple shared tags quirk"
> > +				" not compatible with device mqes %d\n", mqes);
> > +			result = -ENODEV;
> > +			goto disable;
> > +		}
> > +		dev->q_depth = min_t(int, dev->q_depth,
> > +				     mqes - NVME_AQ_DEPTH + 1);
> > +	}
> > +
> >  	/*
> >  	 * Temporary fix for the Apple controller found in the MacBook8,1 and
> >  	 * some MacBook7,1 to avoid controller resets and data loss.
> > @@ -3057,7 +3092,8 @@ static const struct pci_device_id nvme_id_table[] = {
> >  	{ PCI_DEVICE(PCI_VENDOR_ID_APPLE, 0x2003) },
> >  	{ PCI_DEVICE(PCI_VENDOR_ID_APPLE, 0x2005),
> >  		.driver_data = NVME_QUIRK_SINGLE_VECTOR |
> > -				NVME_QUIRK_128_BYTES_SQES },
> > +				NVME_QUIRK_128_BYTES_SQES |
> > +				NVME_QUIRK_SHARED_TAGS },
> >  	{ 0, }
> >  };
> >  MODULE_DEVICE_TABLE(pci, nvme_id_table);
> > 
> > 
> > 
> > _______________________________________________
> > Linux-nvme mailing list
> > Linux-nvme@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-nvme
> > 
> 
> 

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