RE: [PATCH v2 2/7] iommu/vt-d: Multiple descriptors per qi_submit_sync()

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Wednesday, April 15, 2020 1:26 PM
> 
> Extend qi_submit_sync() function to support multiple descriptors.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/dmar.c        | 39 +++++++++++++++++++++++--------------
>  include/linux/intel-iommu.h |  1 +
>  2 files changed, 25 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
> index bb42177e2369..61d049e91f84 100644
> --- a/drivers/iommu/dmar.c
> +++ b/drivers/iommu/dmar.c
> @@ -1157,12 +1157,11 @@ static inline void reclaim_free_desc(struct
> q_inval *qi)
>  	}
>  }
> 
> -static int qi_check_fault(struct intel_iommu *iommu, int index)
> +static int qi_check_fault(struct intel_iommu *iommu, int index, int
> wait_index)
>  {
>  	u32 fault;
>  	int head, tail;
>  	struct q_inval *qi = iommu->qi;
> -	int wait_index = (index + 1) % QI_LENGTH;
>  	int shift = qi_shift(iommu);
> 
>  	if (qi->desc_status[wait_index] == QI_ABORT)
> @@ -1234,12 +1233,12 @@ static int qi_check_fault(struct intel_iommu
> *iommu, int index)
>  int qi_submit_sync(struct intel_iommu *iommu, struct qi_desc *desc,
>  		   unsigned int count, unsigned long options)
>  {
> -	int rc;
>  	struct q_inval *qi = iommu->qi;
> -	int offset, shift, length;
>  	struct qi_desc wait_desc;
>  	int wait_index, index;
>  	unsigned long flags;
> +	int offset, shift;
> +	int rc, i;
> 
>  	if (!qi)
>  		return 0;
> @@ -1248,32 +1247,41 @@ int qi_submit_sync(struct intel_iommu *iommu,
> struct qi_desc *desc,
>  	rc = 0;
> 
>  	raw_spin_lock_irqsave(&qi->q_lock, flags);
> -	while (qi->free_cnt < 3) {
> +	/*
> +	 * Check if we have enough empty slots in the queue to submit,
> +	 * the calculation is based on:
> +	 * # of desc + 1 wait desc + 1 space between head and tail
> +	 */
> +	while (qi->free_cnt < count + 2) {
>  		raw_spin_unlock_irqrestore(&qi->q_lock, flags);
>  		cpu_relax();
>  		raw_spin_lock_irqsave(&qi->q_lock, flags);
>  	}
> 
>  	index = qi->free_head;
> -	wait_index = (index + 1) % QI_LENGTH;
> +	wait_index = (index + count) % QI_LENGTH;
>  	shift = qi_shift(iommu);
> -	length = 1 << shift;
> 
> -	qi->desc_status[index] = qi->desc_status[wait_index] = QI_IN_USE;
> +	for (i = 0; i < count; i++) {
> +		offset = ((index + i) % QI_LENGTH) << shift;
> +		memcpy(qi->desc + offset, &desc[i], 1 << shift);
> +		qi->desc_status[(index + i) % QI_LENGTH] = QI_IN_USE;
> +	}

what about doing one memcpy and leave the loop only for updating
qi status?

> +	qi->desc_status[wait_index] = QI_IN_USE;
> 
> -	offset = index << shift;
> -	memcpy(qi->desc + offset, desc, length);
>  	wait_desc.qw0 = QI_IWD_STATUS_DATA(QI_DONE) |
>  			QI_IWD_STATUS_WRITE | QI_IWD_TYPE;
> +	if (options & QI_OPT_WAIT_DRAIN)
> +		wait_desc.qw0 |= QI_IWD_PRQ_DRAIN;
>  	wait_desc.qw1 = virt_to_phys(&qi->desc_status[wait_index]);
>  	wait_desc.qw2 = 0;
>  	wait_desc.qw3 = 0;
> 
>  	offset = wait_index << shift;
> -	memcpy(qi->desc + offset, &wait_desc, length);
> +	memcpy(qi->desc + offset, &wait_desc, 1 << shift);
> 
> -	qi->free_head = (qi->free_head + 2) % QI_LENGTH;
> -	qi->free_cnt -= 2;
> +	qi->free_head = (qi->free_head + count + 1) % QI_LENGTH;
> +	qi->free_cnt -= count + 1;
> 
>  	/*
>  	 * update the HW tail register indicating the presence of
> @@ -1289,7 +1297,7 @@ int qi_submit_sync(struct intel_iommu *iommu,
> struct qi_desc *desc,
>  		 * a deadlock where the interrupt context can wait
> indefinitely
>  		 * for free slots in the queue.
>  		 */
> -		rc = qi_check_fault(iommu, index);
> +		rc = qi_check_fault(iommu, index, wait_index);
>  		if (rc)
>  			break;
> 
> @@ -1298,7 +1306,8 @@ int qi_submit_sync(struct intel_iommu *iommu,
> struct qi_desc *desc,
>  		raw_spin_lock(&qi->q_lock);
>  	}
> 
> -	qi->desc_status[index] = QI_DONE;
> +	for (i = 0; i < count; i++)
> +		qi->desc_status[(index + i) % QI_LENGTH] = QI_DONE;
> 
>  	reclaim_free_desc(qi);
>  	raw_spin_unlock_irqrestore(&qi->q_lock, flags);
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index ee2d5cdd8339..cca1e5f9aeaa 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -333,6 +333,7 @@ enum {
> 
>  #define QI_IWD_STATUS_DATA(d)	(((u64)d) << 32)
>  #define QI_IWD_STATUS_WRITE	(((u64)1) << 5)
> +#define QI_IWD_PRQ_DRAIN	(((u64)1) << 7)
> 
>  #define QI_IOTLB_DID(did) 	(((u64)did) << 16)
>  #define QI_IOTLB_DR(dr) 	(((u64)dr) << 7)
> --
> 2.17.1