Re: [PATCH v5 4/7] iommu/sva: Stop using ioasid_set for SVA

[Baolu Lu <baolu.lu@linux.intel.com>]

On 3/10/23 6:21 AM, Jacob Pan wrote:
> From: Jason Gunthorpe <jgg@nvidia.com>
> 
> Instead SVA drivers can use a simple global IDA to allocate PASIDs for
> each mm_struct.
> 
> Future work would be to allow drivers using the SVA APIs to reserve global
> PASIDs from this IDA for their internal use, eg with the DMA API PASID
> support.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
> v5:
> 	- Put removing iommu_sva_find() to a separate patch (Kevin)
> 	- Make pasid allocation range to be inclusive (Tina)
> 	- Simplified return code handling (Baolu)
> v4:
> 	- Keep GFP_ATOMIC flag for PASID allocation, will changed to
> 	GFP_KERNEL in a separate patch.
> ---
>   drivers/iommu/iommu-sva.c | 42 +++++++++++++--------------------------
>   drivers/iommu/iommu-sva.h |  2 --
>   2 files changed, 14 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 4f357ef14f04..b75711bdbe97 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -9,47 +9,33 @@
>   #include "iommu-sva.h"
>   
>   static DEFINE_MUTEX(iommu_sva_lock);
> -static DECLARE_IOASID_SET(iommu_sva_pasid);
> +static DEFINE_IDA(iommu_global_pasid_ida);
>   
> -/**
> - * iommu_sva_alloc_pasid - Allocate a PASID for the mm
> - * @mm: the mm
> - * @min: minimum PASID value (inclusive)
> - * @max: maximum PASID value (inclusive)
> - *
> - * Try to allocate a PASID for this mm, or take a reference to the existing one
> - * provided it fits within the [@min, @max] range. On success the PASID is
> - * available in mm->pasid and will be available for the lifetime of the mm.
> - *
> - * Returns 0 on success and < 0 on error.
> - */
> -int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
> +static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
>   {
>   	int ret = 0;
> -	ioasid_t pasid;
>   
> -	if (min == INVALID_IOASID || max == INVALID_IOASID ||
> -	    min == 0 || max < min)
> +	if (!pasid_valid(min) || !pasid_valid(max) ||
> +	     min == 0 || max < min)

No need to change above line.

>   		return -EINVAL;
>   
>   	mutex_lock(&iommu_sva_lock);
>   	/* Is a PASID already associated with this mm? */
>   	if (pasid_valid(mm->pasid)) {
> -		if (mm->pasid < min || mm->pasid >= max)
> +		if (mm->pasid < min || mm->pasid > max)

I forgot why do we need to change above line. But it's better to put
some comments there so that people don't need to dive into
ioasid_alloc() to know the inclusion or exclusion of @min or @max.

>   			ret = -EOVERFLOW;
>   		goto out;
>   	}
>   
> -	pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
> -	if (!pasid_valid(pasid))
> -		ret = -ENOMEM;
> -	else
> -		mm->pasid = pasid;
> +	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max, GFP_ATOMIC);
> +	if (ret < 0)
> +		goto out;
> +	mm->pasid = ret;
> +	ret = 0;
>   out:
>   	mutex_unlock(&iommu_sva_lock);
>   	return ret;
>   }
> -EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
>   
>   /**
>    * iommu_sva_bind_device() - Bind a process address space to a device
> @@ -221,8 +207,8 @@ iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
>   
>   void mm_pasid_drop(struct mm_struct *mm)
>   {
> -	if (pasid_valid(mm->pasid)) {
> -		ioasid_free(mm->pasid);
> -		mm->pasid = INVALID_IOASID;
> -	}
> +	if (likely(!pasid_valid(mm->pasid)))
> +		return;
> +
> +	ida_free(&iommu_global_pasid_ida, mm->pasid);

Any reason why do you drop "mm->pasid = INVALID_IOASID;" here?

>   }
> diff --git a/drivers/iommu/iommu-sva.h b/drivers/iommu/iommu-sva.h
> index 102eae1817a2..c22d0174ad61 100644
> --- a/drivers/iommu/iommu-sva.h
> +++ b/drivers/iommu/iommu-sva.h
> @@ -8,8 +8,6 @@
>   #include <linux/ioasid.h>
>   #include <linux/mm_types.h>
>   
> -int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max);
> -
>   /* I/O Page fault */
>   struct device;
>   struct iommu_fault;

Best regards,
baolu