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SubjectRe: [PATCH 08/11] drm/i915: use vmap in i915_gem_object_map
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On 24/09/2020 14:58, Christoph Hellwig 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@lst.de>
> ---
> 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;
> + 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;
>

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko

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