[RFC PATCH 4/4] iommu: make IOVA domain page size explicit

[leizhen]

On 2014/11/26 1:27, Robin Murphy wrote:
> Systems may contain heterogeneous IOMMUs supporting differing minimum
> page sizes, which may also not be common with the CPU page size.
> Thus it is practical to have an explicit notion of IOVA granularity
> to simplify handling of mapping and allocation constraints.
> 
> As an initial step, move the IOVA page granularity from an implicit
> compile-time constant to a per-domain property so we can make use
> of it in IOVA domain context at runtime. To keep the abstraction tidy,
> extend the little API of inline iova_* helpers to parallel some of the
> equivalent PAGE_* macros.
> 
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> ---
>  drivers/iommu/intel-iommu.c |  9 ++++++---
>  drivers/iommu/iova.c        |  8 ++++++--
>  include/linux/iova.h        | 35 +++++++++++++++++++++++++++++++++--
>  3 files changed, 45 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index daba0c2..d4cf6f0 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -1632,7 +1632,8 @@ static int dmar_init_reserved_ranges(void)
>  	struct iova *iova;
>  	int i;
>  
> -	init_iova_domain(&reserved_iova_list, IOVA_START_PFN, DMA_32BIT_PFN);
> +	init_iova_domain(&reserved_iova_list, VTD_PAGE_SIZE, IOVA_START_PFN,
> +			DMA_32BIT_PFN);
>  
>  	lockdep_set_class(&reserved_iova_list.iova_rbtree_lock,
>  		&reserved_rbtree_key);
> @@ -1690,7 +1691,8 @@ static int domain_init(struct dmar_domain *domain, int guest_width)
>  	int adjust_width, agaw;
>  	unsigned long sagaw;
>  
> -	init_iova_domain(&domain->iovad, IOVA_START_PFN, DMA_32BIT_PFN);
> +	init_iova_domain(&domain->iovad, VTD_PAGE_SIZE, IOVA_START_PFN,
> +			DMA_32BIT_PFN);
>  	domain_reserve_special_ranges(domain);
>  
>  	/* calculate AGAW */
> @@ -4163,7 +4165,8 @@ static int md_domain_init(struct dmar_domain *domain, int guest_width)
>  {
>  	int adjust_width;
>  
> -	init_iova_domain(&domain->iovad, IOVA_START_PFN, DMA_32BIT_PFN);
> +	init_iova_domain(&domain->iovad, VTD_PAGE_SIZE, IOVA_START_PFN,
> +			DMA_32BIT_PFN);
>  	domain_reserve_special_ranges(domain);
>  
>  	/* calculate AGAW */
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index a3dbba8..9e50625 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -55,12 +55,16 @@ void free_iova_mem(struct iova *iova)
>  }
>  
>  void
> -init_iova_domain(struct iova_domain *iovad, unsigned long start_pfn,
> -	unsigned long pfn_32bit)
> +init_iova_domain(struct iova_domain *iovad, unsigned long granule,
> +	unsigned long start_pfn, unsigned long pfn_32bit)
>  {
> +	/* IOMMUs must support at least the CPU page size */
> +	BUG_ON(granule > PAGE_SIZE);

??? BUG_ON(granule < PAGE_SIZE);

> +
>  	spin_lock_init(&iovad->iova_rbtree_lock);
>  	iovad->rbroot = RB_ROOT;
>  	iovad->cached32_node = NULL;
> +	iovad->granule = granule;

Do you need to check granule is 2^n ?

>  	iovad->start_pfn = start_pfn;
>  	iovad->dma_32bit_pfn = pfn_32bit;
>  }
> diff --git a/include/linux/iova.h b/include/linux/iova.h
> index 591b196..3920a19 100644
> --- a/include/linux/iova.h
> +++ b/include/linux/iova.h
> @@ -28,6 +28,7 @@ struct iova_domain {
>  	spinlock_t	iova_rbtree_lock; /* Lock to protect update of rbtree */
>  	struct rb_root	rbroot;		/* iova domain rbtree root */
>  	struct rb_node	*cached32_node; /* Save last alloced node */
> +	unsigned long	granule;	/* pfn granularity for this domain */
>  	unsigned long	start_pfn;	/* Lower limit for this domain */
>  	unsigned long	dma_32bit_pfn;
>  };
> @@ -37,6 +38,36 @@ static inline unsigned long iova_size(struct iova *iova)
>  	return iova->pfn_hi - iova->pfn_lo + 1;
>  }
>  
> +static inline unsigned long iova_shift(struct iova_domain *iovad)
> +{
> +	return __ffs(iovad->granule);

I think it's good to save the result to a struct member. If we caculate it ervertime, it's too slow.

> +}
> +
> +static inline unsigned long iova_mask(struct iova_domain *iovad)
> +{
> +	return iovad->granule - 1;
> +}
> +
> +static inline size_t iova_offset(struct iova_domain *iovad, dma_addr_t iova)
> +{
> +	return iova & iova_mask(iovad);
> +}
> +
> +static inline size_t iova_align(struct iova_domain *iovad, size_t size)
> +{
> +	return ALIGN(size, iovad->granule);
> +}
> +
> +static inline dma_addr_t iova_dma_addr(struct iova_domain *iovad, struct iova *iova)
> +{
> +	return (dma_addr_t)iova->pfn_lo << iova_shift(iovad);
> +}
> +
> +static inline unsigned long iova_pfn(struct iova_domain *iovad, dma_addr_t iova)
> +{
> +	return iova >> iova_shift(iovad);
> +}
> +
>  int iommu_iova_cache_init(void);
>  void iommu_iova_cache_destroy(void);
>  
> @@ -50,8 +81,8 @@ struct iova *alloc_iova(struct iova_domain *iovad, unsigned long size,
>  struct iova *reserve_iova(struct iova_domain *iovad, unsigned long pfn_lo,
>  	unsigned long pfn_hi);
>  void copy_reserved_iova(struct iova_domain *from, struct iova_domain *to);
> -void init_iova_domain(struct iova_domain *iovad, unsigned long start_pfn,
> -	unsigned long pfn_32bit);
> +void init_iova_domain(struct iova_domain *iovad, unsigned long granule,
> +	unsigned long start_pfn, unsigned long pfn_32bit);
>  struct iova *find_iova(struct iova_domain *iovad, unsigned long pfn);
>  void put_iova_domain(struct iova_domain *iovad);
>  struct iova *split_and_remove_iova(struct iova_domain *iovad,
>