Re: [PATCH 5/9] drm/i915/bdw: Reorganize PT allocations

[Imre Deak <imre.deak@intel.com>]

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On Wed, 2014-02-12 at 14:28 -0800, Ben Widawsky wrote:
> The previous allocation mechanism would get 2 contiguous allocations,
> one for the page directories, and one for the page tables. As each page
> table is 1 page, and there are 512 of these per page directory, this
> goes to 1MB. An unfriendly request at best. Worse still, our HW now
       ---^
Fwiw, 2MB.

> supports 4 page directories, and a 2MB allocation is not allowed.
> 
> In order to fix this, this patch attempts to split up each page table
> allocation into a single, discrete allocation. There is nothing really
> fancy about the patch itself, it just has to manage an extra pointer
> indirection, and have a fancier bit of logic to free up the pages.
> 
> To accommodate some of the added complexity, two new helpers are
> introduced to allocate, and free the page table pages.
> 
> NOTE: I really wanted to split the way we do allocations, and the way in
> which we identify the page table/page directory being used. I found
> splitting this functionality up to be too unwieldy. I apologize in
> advance to the reviewer. I'd recommend looking at the result, rather
> than the diff.
> 
> v2/NOTE2: This patch predated commit:
> 6f1cc993518462ccf039e195fabd47e7aa5bfd13
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date:   Tue Dec 31 15:50:31 2013 +0000
> 
>     drm/i915: Avoid dereference past end of page arr
> 
> It fixed the same issue as that patch, but because of the limbo state of
> PPGTT, Chris patch was merged instead. The excess churn is a result of
> my using my original patch, which has my preferred naming. Primarily
> act_* is changed to which_*, but it's mostly the same otherwise. I've
> kept the convention Chris used for the pte wrap (I had something
> slightly different, and broken - but fixable)
> 
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_drv.h     |   5 +-
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 127 ++++++++++++++++++++++++++++--------
>  2 files changed, 103 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 2ebad96..d9a6327 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -691,6 +691,7 @@ struct i915_gtt {
>  };
>  #define gtt_total_entries(gtt) ((gtt).base.total >> PAGE_SHIFT)
>  
> +#define GEN8_LEGACY_PDPS 4
>  struct i915_hw_ppgtt {
>  	struct i915_address_space base;
>  	struct kref ref;
> @@ -698,14 +699,14 @@ struct i915_hw_ppgtt {
>  	unsigned num_pd_entries;
>  	union {
>  		struct page **pt_pages;
> -		struct page *gen8_pt_pages;
> +		struct page **gen8_pt_pages[GEN8_LEGACY_PDPS];
>  	};
>  	struct page *pd_pages;
>  	int num_pd_pages;
>  	int num_pt_pages;
>  	union {
>  		uint32_t pd_offset;
> -		dma_addr_t pd_dma_addr[4];
> +		dma_addr_t pd_dma_addr[GEN8_LEGACY_PDPS];
>  	};
>  	union {
>  		dma_addr_t *pt_dma_addr;
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 5bfc6ff..5299acc 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -64,7 +64,19 @@ typedef gen8_gtt_pte_t gen8_ppgtt_pde_t;
>  
>  #define GEN8_PTES_PER_PAGE		(PAGE_SIZE / sizeof(gen8_gtt_pte_t))
>  #define GEN8_PDES_PER_PAGE		(PAGE_SIZE / sizeof(gen8_ppgtt_pde_t))
> -#define GEN8_LEGACY_PDPS		4
> +
> +/* GEN8 legacy style addressis defined as a 3 level page table:
> + * 31:30 | 29:21 | 20:12 |  11:0
> + * PDPE  |  PDE  |  PTE  | offset
> + * The difference as compared to normal x86 3 level page table is the PDPEs are
> + * programmed via register.
> + */
> +#define GEN8_PDPE_SHIFT			30
> +#define GEN8_PDPE_MASK			0x3
> +#define GEN8_PDE_SHIFT			21
> +#define GEN8_PDE_MASK			0x1ff
> +#define GEN8_PTE_SHIFT			12
> +#define GEN8_PTE_MASK			0x1ff
>  
>  #define PPAT_UNCACHED_INDEX		(_PAGE_PWT | _PAGE_PCD)
>  #define PPAT_CACHED_PDE_INDEX		0 /* WB LLC */
> @@ -261,32 +273,36 @@ static void gen8_ppgtt_clear_range(struct i915_address_space *vm,
>  	struct i915_hw_ppgtt *ppgtt =
>  		container_of(vm, struct i915_hw_ppgtt, base);
>  	gen8_gtt_pte_t *pt_vaddr, scratch_pte;
> -	unsigned first_entry = start >> PAGE_SHIFT;
> +	unsigned which_pdpe = start >> GEN8_PDPE_SHIFT & GEN8_PDPE_MASK;
> +	unsigned which_pde = start >> GEN8_PDE_SHIFT & GEN8_PDE_MASK;
> +	unsigned which_pte = start >> GEN8_PTE_SHIFT & GEN8_PTE_MASK;
>  	unsigned num_entries = length >> PAGE_SHIFT;
> -	unsigned act_pt = first_entry / GEN8_PTES_PER_PAGE;
> -	unsigned first_pte = first_entry % GEN8_PTES_PER_PAGE;
>  	unsigned last_pte, i;
>  
>  	scratch_pte = gen8_pte_encode(ppgtt->base.scratch.addr,
>  				      I915_CACHE_LLC, use_scratch);
>  
>  	while (num_entries) {
> -		struct page *page_table = &ppgtt->gen8_pt_pages[act_pt];
> +		struct page *page_table = ppgtt->gen8_pt_pages[which_pdpe][which_pde];
>  
> -		last_pte = first_pte + num_entries;
> +		last_pte = which_pte + num_entries;
>  		if (last_pte > GEN8_PTES_PER_PAGE)
>  			last_pte = GEN8_PTES_PER_PAGE;
>  
>  		pt_vaddr = kmap_atomic(page_table);
>  
> -		for (i = first_pte; i < last_pte; i++)
> +		for (i = which_pte; i < last_pte; i++) {
>  			pt_vaddr[i] = scratch_pte;
> +			num_entries--;
> +			BUG_ON(num_entries < 0);

num_entries is unsigned.

> +		}
>  
>  		kunmap_atomic(pt_vaddr);
>  
> -		num_entries -= last_pte - first_pte;
> -		first_pte = 0;
> -		act_pt++;
> +		which_pte = 0;
> +		if (which_pde + 1 == GEN8_PDES_PER_PAGE)
> +			which_pdpe++;
> +		which_pde = (which_pde + 1) & GEN8_PDE_MASK;
>  	}
>  }
>  
> @@ -298,39 +314,57 @@ static void gen8_ppgtt_insert_entries(struct i915_address_space *vm,
>  	struct i915_hw_ppgtt *ppgtt =
>  		container_of(vm, struct i915_hw_ppgtt, base);
>  	gen8_gtt_pte_t *pt_vaddr;
> -	unsigned first_entry = start >> PAGE_SHIFT;
> -	unsigned act_pt = first_entry / GEN8_PTES_PER_PAGE;
> -	unsigned act_pte = first_entry % GEN8_PTES_PER_PAGE;
> +	unsigned which_pdpe = start >> GEN8_PDPE_SHIFT & GEN8_PDPE_MASK;
> +	unsigned which_pde = start >> GEN8_PDE_SHIFT & GEN8_PDE_MASK;
> +	unsigned which_pte = start >> GEN8_PTE_SHIFT & GEN8_PTE_MASK;
>  	struct sg_page_iter sg_iter;
>  
>  	pt_vaddr = NULL;
> +
>  	for_each_sg_page(pages->sgl, &sg_iter, pages->nents, 0) {
> +		if (WARN_ON(which_pdpe >= GEN8_LEGACY_PDPS))
> +			break;
> +
>  		if (pt_vaddr == NULL)
> -			pt_vaddr = kmap_atomic(&ppgtt->gen8_pt_pages[act_pt]);
> +			pt_vaddr = kmap_atomic(ppgtt->gen8_pt_pages[which_pdpe][which_pde]);
>  
> -		pt_vaddr[act_pte] =
> +		pt_vaddr[which_pte] =
>  			gen8_pte_encode(sg_page_iter_dma_address(&sg_iter),
>  					cache_level, true);
> -		if (++act_pte == GEN8_PTES_PER_PAGE) {
> +		if (++which_pte == GEN8_PTES_PER_PAGE) {
>  			kunmap_atomic(pt_vaddr);
>  			pt_vaddr = NULL;
> -			act_pt++;
> -			act_pte = 0;
> +			if (which_pde + 1 == GEN8_PDES_PER_PAGE)
> +				which_pdpe++;

Afaics which_pde = (which_pde + 1) & GEN8_PDE_MASK; is missing here.

> +			which_pte = 0;



>  		}
>  	}
>  	if (pt_vaddr)
>  		kunmap_atomic(pt_vaddr);
>  }
>  
> -static void gen8_ppgtt_free(struct i915_hw_ppgtt *ppgtt)
> +static void gen8_free_page_tables(struct page **pt_pages)
> +{
> +	int i;
> +
> +	if (pt_pages == NULL)
> +		return;
> +
> +	for (i = 0; i < GEN8_PDES_PER_PAGE; i++)
> +		if (pt_pages[i])
> +			__free_pages(pt_pages[i], 0);
> +}
> +
> +static void gen8_ppgtt_free(const struct i915_hw_ppgtt *ppgtt)
>  {
>  	int i;
>  
> -	for (i = 0; i < ppgtt->num_pd_pages ; i++)
> +	for (i = 0; i < ppgtt->num_pd_pages; i++) {
> +		gen8_free_page_tables(ppgtt->gen8_pt_pages[i]);
>  		kfree(ppgtt->gen8_pt_dma_addr[i]);
> +	}
>  
>  	kfree(ppgtt->gen8_pt_dma_addr);
> -	__free_pages(ppgtt->gen8_pt_pages, get_order(ppgtt->num_pt_pages << PAGE_SHIFT));
>  	__free_pages(ppgtt->pd_pages, get_order(ppgtt->num_pd_pages << PAGE_SHIFT));
>  }
>  
> @@ -369,20 +403,59 @@ static void gen8_ppgtt_cleanup(struct i915_address_space *vm)
>  	gen8_ppgtt_free(ppgtt);
>  }
>  
> +static struct page **__gen8_alloc_page_tables(void)
> +{
> +	struct page **pt_pages;
> +	int i;
> +
> +	pt_pages = kcalloc(GEN8_PDES_PER_PAGE, sizeof(struct page *), GFP_KERNEL);
> +	if (!pt_pages)
> +		return ERR_PTR(-ENOMEM);
> +
> +	for (i = 0; i < GEN8_PDES_PER_PAGE; i++) {
> +		pt_pages[i] = alloc_page(GFP_KERNEL);
> +		if (!pt_pages[i])
> +			goto bail;
> +	}
> +
> +	return pt_pages;
> +
> +bail:
> +	gen8_free_page_tables(pt_pages);
> +	kfree(pt_pages);
> +	return ERR_PTR(-ENOMEM);
> +}
> +
>  static int gen8_ppgtt_allocate_page_tables(struct i915_hw_ppgtt *ppgtt,
>  					   const int max_pdp)
>  {
> -	struct page *pt_pages;
> +	struct page **pt_pages[GEN8_LEGACY_PDPS];
>  	const int num_pt_pages = GEN8_PDES_PER_PAGE * max_pdp;
> +	int i, ret;
>  
> -	pt_pages = alloc_pages(GFP_KERNEL, get_order(num_pt_pages << PAGE_SHIFT));
> -	if (!pt_pages)
> -		return -ENOMEM;
> +	for (i = 0; i < max_pdp; i++) {
> +		pt_pages[i] = __gen8_alloc_page_tables();
> +		if (IS_ERR(pt_pages[i])) {
> +			ret = PTR_ERR(pt_pages[i]);
> +			goto unwind_out;
> +		}
> +	}
> +
> +	/* NB: Avoid touching gen8_pt_pages until last to keep the allocation,
> +	 * "atomic" - for cleanup purposes.
> +	 */
> +	for (i = 0; i < max_pdp; i++)
> +		ppgtt->gen8_pt_pages[i] = pt_pages[i];
>  
> -	ppgtt->gen8_pt_pages = pt_pages;
>  	ppgtt->num_pt_pages = 1 << get_order(num_pt_pages << PAGE_SHIFT);
>  
>  	return 0;
> +
> +unwind_out:
> +	while(i--)
> +		gen8_free_page_tables(pt_pages[i]);

I guess Ville commented on this issue, but pt_pages would be leaked
here.

> +
> +	return ret;
>  }
>  
>  static int gen8_ppgtt_allocate_dma(struct i915_hw_ppgtt *ppgtt)
> @@ -475,7 +548,7 @@ static int gen8_ppgtt_setup_page_tables(struct i915_hw_ppgtt *ppgtt,
>  	struct page *p;
>  	int ret;
>  
> -	p = &ppgtt->gen8_pt_pages[pd * GEN8_PDES_PER_PAGE + pt];
> +	p = ppgtt->gen8_pt_pages[pd][pt];
>  	pt_addr = pci_map_page(ppgtt->base.dev->pdev,
>  			       p, 0, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
>  	ret = pci_dma_mapping_error(ppgtt->base.dev->pdev, pt_addr);


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