Re: [PATCH v2 2/3] iommu/sva: Stop using ioasid_set for SVA

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Mon, Feb 13, 2023 at 10:44:13PM -0800, 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>
> ---
> v2: minor fixes
> 	- let idxd driver use iommu.h for ioasid_t
> 	- return 0 after mm_pasid_set()
> ---
>  drivers/dma/idxd/idxd.h   |  1 +
>  drivers/iommu/iommu-sva.c | 53 +++++++++++----------------------------
>  drivers/iommu/iommu-sva.h |  3 ---
>  include/linux/sched/mm.h  |  8 +-----
>  4 files changed, 17 insertions(+), 48 deletions(-)
> 
> diff --git a/drivers/dma/idxd/idxd.h b/drivers/dma/idxd/idxd.h
> index 7ced8d283d98..417e602a46b6 100644
> --- a/drivers/dma/idxd/idxd.h
> +++ b/drivers/dma/idxd/idxd.h
> @@ -13,6 +13,7 @@
>  #include <linux/ioasid.h>
>  #include <linux/bitmap.h>
>  #include <linux/perf_event.h>
> +#include <linux/iommu.h>

Unrelated 

>  #include <uapi/linux/idxd.h>
>  #include "registers.h"
>  
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 24bf9b2b58aa..8fb6f1867af3 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -9,24 +9,11 @@
>  #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 ||
>  	    min == 0 || max < min)
> @@ -37,39 +24,29 @@ 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;
>  		goto out;
>  	}
>  
> -	pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
> -	if (!pasid_valid(pasid))
> -		ret = -ENOMEM;
> -	else
> -		mm_pasid_set(mm, pasid);
> +	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max, GFP_KERNEL);
> +	if (ret < min)

Just check ret < 0

> +		goto out;
> +	mm_pasid_set(mm, 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)
> +void mm_pasid_drop(struct mm_struct *mm)
>  {
> -	return mmget_not_zero(mm);
> -}
> +	pr_alert("%s %d", __func__, mm->pasid);

Debug print

Thanks,
Jean

> +	if (likely(!pasid_valid(mm->pasid)))
> +		return;
>  
> -/**
> - * 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);
> +	ida_free(&iommu_global_pasid_ida, mm->pasid);
>  }
> -EXPORT_SYMBOL_GPL(iommu_sva_find);
>  
>  /**
>   * iommu_sva_bind_device() - Bind a process address space to a device
> 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;
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 2a243616f222..cdc138086230 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -463,13 +463,7 @@ static inline void mm_pasid_set(struct mm_struct *mm, u32 pasid)
>  	mm->pasid = pasid;
>  }
>  
> -static inline void mm_pasid_drop(struct mm_struct *mm)
> -{
> -	if (pasid_valid(mm->pasid)) {
> -		ioasid_free(mm->pasid);
> -		mm->pasid = INVALID_IOASID;
> -	}
> -}
> +void mm_pasid_drop(struct mm_struct *mm);
>  #else
>  static inline void mm_pasid_init(struct mm_struct *mm) {}
>  static inline void mm_pasid_set(struct mm_struct *mm, u32 pasid) {}
> -- 
> 2.25.1
>