[PATCH] drm/amd/amdgpu: solve the issue of allocate continuous pages under xen dom0

[Liu, Aaron]

[AMD Official Use Only - General]

Reviewed-by: Aaron Liu <aaron.liu at amd.com>

--
Best Regards
Aaron Liu

> -----Original Message-----
> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of
> Shane Xiao
> Sent: Thursday, September 22, 2022 3:12 PM
> To: amd-gfx at lists.freedesktop.org
> Cc: Xiao, Shane <shane.xiao at amd.com>
> Subject: [PATCH] drm/amd/amdgpu: solve the issue of allocate continuous
> pages under xen dom0
> 
> [Why]
> sg_alloc_table_from_pages alloc too large continuous PFN pages under xen
> dom0.
> However, xen should check continuous MFN pages in
> range_straddles_page_boundary.
> When range_straddles_page_boundary return false, some cases fall back
> into swiotlb process and the continuous allocable page is not enough.
> 
> [How]
> In fact, xen swiotlb set max_segment default value as UINT_MAX and
> xen_swiotlb_init_early already change the value to PAGE_SIZE under xen
> dom0.
> However amdgpu driver doesn't use the value, which may cause issue such
> as swiotlb buffer full. Add amd_sg_segment_size according to iommu setting,
> the details are as follows:
> 	iommu setting		|	amd_sg_segment_size
> -------------------------------------------------------------------------------
> 	iommu=on		|	UINT_MAX
>     iommu=off && swiotlb on	|	IO_TLB_DEFAULT_SIZE(64M)
> 	xen_swiotlb on		|	PAGE_SIZE(4K)
> -------------------------------------------------------------------------------
> 
> Signed-off-by: Shane Xiao <shane.xiao at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 22
> ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 134575a3893c..d081fcd22d6b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -80,6 +80,23 @@ static int amdgpu_ttm_init_on_chip(struct
> amdgpu_device *adev,
>  				  false, size_in_page);
>  }
> 
> +static inline unsigned int amdgpu_sg_segment_size(void) {
> +	unsigned int size = swiotlb_max_segment();
> +
> +	/* size=0 when amd iommu enabled */
> +	if (size == 0)
> +		size = UINT_MAX;
> +
> +	size = rounddown(size, PAGE_SIZE);
> +	/* swiotlb_max_segment_size can return 1 byte when it means one
> page. */
> +	if (size < PAGE_SIZE)
> +		size = PAGE_SIZE;
> +
> +	return size;
> +}
> +
> +
>  /**
>   * amdgpu_evict_flags - Compute placement flags
>   *
> @@ -760,9 +777,10 @@ static int amdgpu_ttm_tt_pin_userptr(struct
> ttm_device *bdev,
>  	int r;
> 
>  	/* Allocate an SG array and squash pages into it */
> -	r = sg_alloc_table_from_pages(ttm->sg, ttm->pages, ttm->num_pages,
> 0,
> -				      (u64)ttm->num_pages << PAGE_SHIFT,
> +	r = sg_alloc_table_from_pages_segment(ttm->sg, ttm->pages, ttm-
> >num_pages, 0,
> +				      (u64)ttm->num_pages << PAGE_SHIFT,
> amdgpu_sg_segment_size(),
>  				      GFP_KERNEL);
> +
>  	if (r)
>  		goto release_sg;
> 
> --
> 2.25.1