Re: [Intel-gfx] [PATCH 08/11] drm/i915: use vmap in i915_gem_object_map

[Matthew Auld]

On Thu, 24 Sep 2020 at 14:59, Christoph Hellwig <hch@xxxxxx> wrote:
>
> i915_gem_object_map implements fairly low-level vmap functionality in
> a driver.  Split it into two helpers, one for remapping kernel memory
> which can use vmap, and one for I/O memory that uses vmap_pfn.
>
> The only practical difference is that alloc_vm_area prefeaults the
> vmalloc area PTEs, which doesn't seem to be required here for the
> kernel memory case (and could be added to vmap using a flag if actually
> required).
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  drivers/gpu/drm/i915/Kconfig              |   1 +
>  drivers/gpu/drm/i915/gem/i915_gem_pages.c | 126 ++++++++++------------
>  2 files changed, 59 insertions(+), 68 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> index 9afa5c4a6bf006..1e1cb245fca778 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -25,6 +25,7 @@ config DRM_I915
>         select CRC32
>         select SND_HDA_I915 if SND_HDA_CORE
>         select CEC_CORE if CEC_NOTIFIER
> +       select VMAP_PFN
>         help
>           Choose this option if you have a system that has "Intel Graphics
>           Media Accelerator" or "HD Graphics" integrated graphics,
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> index 6550c0bc824ea2..b519417667eb4b 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> @@ -232,34 +232,21 @@ int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
>         return err;
>  }
>
> -static inline pte_t iomap_pte(resource_size_t base,
> -                             dma_addr_t offset,
> -                             pgprot_t prot)
> -{
> -       return pte_mkspecial(pfn_pte((base + offset) >> PAGE_SHIFT, prot));
> -}
> -
>  /* The 'mapping' part of i915_gem_object_pin_map() below */
> -static void *i915_gem_object_map(struct drm_i915_gem_object *obj,
> -                                enum i915_map_type type)
> +static void *i915_gem_object_map_page(struct drm_i915_gem_object *obj,
> +               enum i915_map_type type)
>  {
> -       unsigned long n_pte = obj->base.size >> PAGE_SHIFT;
> -       struct sg_table *sgt = obj->mm.pages;
> -       pte_t *stack[32], **mem;
> -       struct vm_struct *area;
> +       unsigned long n_pages = obj->base.size >> PAGE_SHIFT, i;
> +       struct page *stack[32], **pages = stack, *page;
> +       struct sgt_iter iter;
>         pgprot_t pgprot;
> +       void *vaddr;
>
> -       if (!i915_gem_object_has_struct_page(obj) && type != I915_MAP_WC)
> -               return NULL;
> -
> -       if (GEM_WARN_ON(type == I915_MAP_WC &&
> -                       !static_cpu_has(X86_FEATURE_PAT)))
> -               return NULL;
> -
> -       /* A single page can always be kmapped */
> -       if (n_pte == 1 && type == I915_MAP_WB) {
> -               struct page *page = sg_page(sgt->sgl);
> -
> +       switch (type) {
> +       default:
> +               MISSING_CASE(type);
> +               fallthrough;    /* to use PAGE_KERNEL anyway */
> +       case I915_MAP_WB:
>                 /*
>                  * On 32b, highmem using a finite set of indirect PTE (i.e.
>                  * vmap) to provide virtual mappings of the high pages.
> @@ -277,30 +264,8 @@ static void *i915_gem_object_map(struct drm_i915_gem_object *obj,
>                  * So if the page is beyond the 32b boundary, make an explicit
>                  * vmap.
>                  */
> -               if (!PageHighMem(page))
> -                       return page_address(page);
> -       }
> -
> -       mem = stack;
> -       if (n_pte > ARRAY_SIZE(stack)) {
> -               /* Too big for stack -- allocate temporary array instead */
> -               mem = kvmalloc_array(n_pte, sizeof(*mem), GFP_KERNEL);
> -               if (!mem)
> -                       return NULL;
> -       }
> -
> -       area = alloc_vm_area(obj->base.size, mem);
> -       if (!area) {
> -               if (mem != stack)
> -                       kvfree(mem);
> -               return NULL;
> -       }
> -
> -       switch (type) {
> -       default:
> -               MISSING_CASE(type);
> -               fallthrough;    /* to use PAGE_KERNEL anyway */
> -       case I915_MAP_WB:
> +               if (n_pages == 1 && !PageHighMem(sg_page(obj->mm.pages->sgl)))
> +                       return page_address(sg_page(obj->mm.pages->sgl));
>                 pgprot = PAGE_KERNEL;
>                 break;
>         case I915_MAP_WC:
> @@ -308,30 +273,49 @@ static void *i915_gem_object_map(struct drm_i915_gem_object *obj,
>                 break;
>         }
>
> -       if (i915_gem_object_has_struct_page(obj)) {
> -               struct sgt_iter iter;
> -               struct page *page;
> -               pte_t **ptes = mem;
> +       if (n_pages > ARRAY_SIZE(stack)) {
> +               /* Too big for stack -- allocate temporary array instead */
> +               pages = kvmalloc_array(n_pages, sizeof(*pages), GFP_KERNEL);
> +               if (!pages)
> +                       return NULL;
> +       }
>
> -               for_each_sgt_page(page, iter, sgt)
> -                       **ptes++ = mk_pte(page, pgprot);
> -       } else {
> -               resource_size_t iomap;
> -               struct sgt_iter iter;
> -               pte_t **ptes = mem;
> -               dma_addr_t addr;
> +       i = 0;
> +       for_each_sgt_page(page, iter, obj->mm.pages)
> +               pages[i++] = page;
> +       vaddr = vmap(pages, n_pages, 0, pgprot);
> +       if (pages != stack)
> +               kvfree(pages);
> +       return vaddr;
> +}
>
> -               iomap = obj->mm.region->iomap.base;
> -               iomap -= obj->mm.region->region.start;
> +static void *i915_gem_object_map_pfn(struct drm_i915_gem_object *obj,
> +               enum i915_map_type type)
> +{
> +       resource_size_t iomap = obj->mm.region->iomap.base -
> +               obj->mm.region->region.start;
> +       unsigned long n_pfn = obj->base.size >> PAGE_SHIFT;
> +       unsigned long stack[32], *pfns = stack, i;
> +       struct sgt_iter iter;
> +       dma_addr_t addr;
> +       void *vaddr;
> +
> +       if (type != I915_MAP_WC)
> +               return NULL;
>
> -               for_each_sgt_daddr(addr, iter, sgt)
> -                       **ptes++ = iomap_pte(iomap, addr, pgprot);
> +       if (n_pfn > ARRAY_SIZE(stack)) {
> +               /* Too big for stack -- allocate temporary array instead */
> +               pfns = kvmalloc_array(n_pfn, sizeof(*pfns), GFP_KERNEL);
> +               if (!pfns)
> +                       return NULL;
>         }
>
> -       if (mem != stack)
> -               kvfree(mem);
> -
> -       return area->addr;
> +       for_each_sgt_daddr(addr, iter, obj->mm.pages)
> +               pfns[i++] = (iomap + addr) >> PAGE_SHIFT;

Missing the i = 0 fix from Dan?

> +       vaddr = vmap_pfn(pfns, n_pfn, pgprot_writecombine(PAGE_KERNEL_IO));
> +       if (pfns != stack)
> +               kvfree(pfns);
> +       return vaddr;
>  }
>
>  /* get, pin, and map the pages of the object into kernel space */
> @@ -383,7 +367,13 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
>         }
>
>         if (!ptr) {
> -               ptr = i915_gem_object_map(obj, type);
> +               if (GEM_WARN_ON(type == I915_MAP_WC &&
> +                               !static_cpu_has(X86_FEATURE_PAT)))
> +                       ptr = NULL;
> +               else if (i915_gem_object_has_struct_page(obj))
> +                       ptr = i915_gem_object_map_page(obj, type);
> +               else
> +                       ptr = i915_gem_object_map_pfn(obj, type);
>                 if (!ptr) {
>                         err = -ENOMEM;
>                         goto err_unpin;
> --
> 2.28.0
>
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