Re: [PATCH 05/18] dma: Provide an interface to allow allocate IOVA

[Srinivasulu Thanneeru <dev.srinivasulu@gmail.com>]

On Sun, Oct 27, 2024 at 10:23 PM Leon Romanovsky <leon@kernel.org> wrote:
>
> From: Leon Romanovsky <leonro@nvidia.com>
>
> The existing .map_page() callback provides both allocating of IOVA
> and linking DMA pages. That combination works great for most of the
> callers who use it in control paths, but is less effective in fast
> paths where there may be multiple calls to map_page().

Can you please share perf stats with this patch in fast path, if available?

> These advanced callers already manage their data in some sort of
> database and can perform IOVA allocation in advance, leaving range
> linkage operation to be in fast path.
>
> Provide an interface to allocate/deallocate IOVA and next patch
> link/unlink DMA ranges to that specific IOVA.
>
> The API is exported from dma-iommu as it is the only implementation
> supported, the namespace is clearly different from iommu_* functions
> which are not allowed to be used. This code layout allows us to save
> function call per API call used in datapath as well as a lot of boilerplate
> code.
>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
>  drivers/iommu/dma-iommu.c   | 79 +++++++++++++++++++++++++++++++++++++
>  include/linux/dma-mapping.h | 15 +++++++
>  2 files changed, 94 insertions(+)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index c422e36c0d66..0644152c5aad 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1745,6 +1745,85 @@ size_t iommu_dma_max_mapping_size(struct device *dev)
>         return SIZE_MAX;
>  }
>
> +static bool iommu_dma_iova_alloc(struct device *dev,
> +               struct dma_iova_state *state, phys_addr_t phys, size_t size)
> +{
> +       struct iommu_domain *domain = iommu_get_dma_domain(dev);
> +       struct iommu_dma_cookie *cookie = domain->iova_cookie;
> +       struct iova_domain *iovad = &cookie->iovad;
> +       size_t iova_off = iova_offset(iovad, phys);
> +       dma_addr_t addr;
> +
> +       if (WARN_ON_ONCE(!size))
> +               return false;
> +       if (WARN_ON_ONCE(size & DMA_IOVA_USE_SWIOTLB))
> +               return false;
> +
> +       addr = iommu_dma_alloc_iova(domain,
> +                       iova_align(iovad, size + iova_off),
> +                       dma_get_mask(dev), dev);
> +       if (!addr)
> +               return false;
> +
> +       state->addr = addr + iova_off;
> +       state->__size = size;
> +       return true;
> +}
> +
> +/**
> + * dma_iova_try_alloc - Try to allocate an IOVA space
> + * @dev: Device to allocate the IOVA space for
> + * @state: IOVA state
> + * @phys: physical address
> + * @size: IOVA size
> + *
> + * Check if @dev supports the IOVA-based DMA API, and if yes allocate IOVA space
> + * for the given base address and size.
> + *
> + * Note: @phys is only used to calculate the IOVA alignment. Callers that always
> + * do PAGE_SIZE aligned transfers can safely pass 0 here.
> + *
> + * Returns %true if the IOVA-based DMA API can be used and IOVA space has been
> + * allocated, or %false if the regular DMA API should be used.
> + */
> +bool dma_iova_try_alloc(struct device *dev, struct dma_iova_state *state,
> +               phys_addr_t phys, size_t size)
> +{
> +       memset(state, 0, sizeof(*state));
> +       if (!use_dma_iommu(dev))
> +               return false;
> +       if (static_branch_unlikely(&iommu_deferred_attach_enabled) &&
> +           iommu_deferred_attach(dev, iommu_get_domain_for_dev(dev)))
> +               return false;
> +       return iommu_dma_iova_alloc(dev, state, phys, size);
> +}
> +EXPORT_SYMBOL_GPL(dma_iova_try_alloc);
> +
> +/**
> + * dma_iova_free - Free an IOVA space
> + * @dev: Device to free the IOVA space for
> + * @state: IOVA state
> + *
> + * Undoes a successful dma_try_iova_alloc().
> + *
> + * Note that all dma_iova_link() calls need to be undone first.  For callers
> + * that never call dma_iova_unlink(), dma_iova_destroy() can be used instead
> + * which unlinks all ranges and frees the IOVA space in a single efficient
> + * operation.
> + */
> +void dma_iova_free(struct device *dev, struct dma_iova_state *state)
> +{
> +       struct iommu_domain *domain = iommu_get_dma_domain(dev);
> +       struct iommu_dma_cookie *cookie = domain->iova_cookie;
> +       struct iova_domain *iovad = &cookie->iovad;
> +       size_t iova_start_pad = iova_offset(iovad, state->addr);
> +       size_t size = dma_iova_size(state);
> +
> +       iommu_dma_free_iova(cookie, state->addr - iova_start_pad,
> +                       iova_align(iovad, size + iova_start_pad), NULL);
> +}
> +EXPORT_SYMBOL_GPL(dma_iova_free);
> +
>  void iommu_setup_dma_ops(struct device *dev)
>  {
>         struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 6075e0708deb..817f11bce7bc 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -11,6 +11,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/bug.h>
>  #include <linux/mem_encrypt.h>
> +#include <linux/iommu.h>
>
>  /**
>   * List of possible attributes associated with a DMA mapping. The semantics
> @@ -77,6 +78,7 @@
>  #define DMA_BIT_MASK(n)        (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
>
>  struct dma_iova_state {
> +       dma_addr_t addr;
>         size_t __size;
>  };
>
> @@ -307,11 +309,24 @@ static inline bool dma_use_iova(struct dma_iova_state *state)
>  {
>         return state->__size != 0;
>  }
> +
> +bool dma_iova_try_alloc(struct device *dev, struct dma_iova_state *state,
> +               phys_addr_t phys, size_t size);
> +void dma_iova_free(struct device *dev, struct dma_iova_state *state);
>  #else /* CONFIG_IOMMU_DMA */
>  static inline bool dma_use_iova(struct dma_iova_state *state)
>  {
>         return false;
>  }
> +static inline bool dma_iova_try_alloc(struct device *dev,
> +               struct dma_iova_state *state, phys_addr_t phys, size_t size)
> +{
> +       return false;
> +}
> +static inline void dma_iova_free(struct device *dev,
> +               struct dma_iova_state *state)
> +{
> +}
>  #endif /* CONFIG_IOMMU_DMA */
>
>  #if defined(CONFIG_HAS_DMA) && defined(CONFIG_DMA_NEED_SYNC)
> --
> 2.46.2
>
>