Re: [PATCH v4 3/6] iommu/sva: Stop using ioasid_set for SVA

[Baolu Lu]

On 2023/3/2 7:56, Jacob Pan wrote:
> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
> v4:
> 	- Keep GFP_ATOMIC flag for PASID allocation, will changed to
> 	GFP_KERNEL in a separate patch.
> ---
>   drivers/iommu/iommu-sva.c | 62 ++++++++++-----------------------------
>   drivers/iommu/iommu-sva.h |  3 --
>   2 files changed, 15 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 376b2a9e2543..297852ae5e7c 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -9,26 +9,13 @@
>   #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;
> +	int ret;
>   
> -	if (min == INVALID_IOASID || max == INVALID_IOASID ||
> +	if (min == IOMMU_PASID_INVALID || max == IOMMU_PASID_INVALID ||
>   	    min == 0 || max < min)

It's irrelevant to this patch. Just out of curiosity, why do we need to
exclude PASID 0 here? I just had a quick look at PCI spec section 6.20.
The spec does not state that PASID 0 is invalid.

>   		return -EINVAL;
>   
> @@ -37,39 +24,20 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
>   	if (pasid_valid(mm->pasid)) {
>   		if (mm->pasid < min || mm->pasid >= max)
>   			ret = -EOVERFLOW;
> +		else
> +			ret = 0;

Nit:

If you didn't change "int ret = 0" to "int ret", we don't need above two
lines. Did I miss anything?

>   		goto out;
>   	}
>   
> -	pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
> -	if (!pasid_valid(pasid))
> -		ret = -ENOMEM;
> -	else
> -		mm->pasid = ret;
> +	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max, GFP_ATOMIC);
> +	if (ret < min)

Nit:
	    ret < 0?

ida_alloc_range() returns negative error number on failure.

> +		goto out;
> +	mm->pasid = ret;
> +	ret = 0;
>   out:
>   	mutex_unlock(&iommu_sva_lock);
>   	return ret;
>   }
> -EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
> -
> -/* ioasid_find getter() requires a void * argument */
> -static bool __mmget_not_zero(void *mm)
> -{
> -	return mmget_not_zero(mm);
> -}
> -
> -/**
> - * iommu_sva_find() - Find mm associated to the given PASID
> - * @pasid: Process Address Space ID assigned to the mm
> - *
> - * On success a reference to the mm is taken, and must be released with mmput().
> - *
> - * Returns the mm corresponding to this PASID, or an error if not found.
> - */
> -struct mm_struct *iommu_sva_find(ioasid_t pasid)
> -{
> -	return ioasid_find(&iommu_sva_pasid, pasid, __mmget_not_zero);
> -}
> -EXPORT_SYMBOL_GPL(iommu_sva_find);

Removing iommu_sva_find() has nothing to do with the intention of this
patch. Perhaps make it in a separated patch?

>   
>   /**
>    * iommu_sva_bind_device() - Bind a process address space to a device
> @@ -241,8 +209,8 @@ 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)))

Why is this a likely?

> +		return;
> +
> +	ida_free(&iommu_global_pasid_ida, mm->pasid);
>   }
> diff --git a/drivers/iommu/iommu-sva.h b/drivers/iommu/iommu-sva.h
> index 7215a761b962..c22d0174ad61 100644
> --- a/drivers/iommu/iommu-sva.h
> +++ b/drivers/iommu/iommu-sva.h
> @@ -8,9 +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);
> -struct mm_struct *iommu_sva_find(ioasid_t pasid);
> -
>   /* I/O Page fault */
>   struct device;
>   struct iommu_fault;

Best regards,
baolu