linux-kernel - Re: [PATCH AUTOSEL 6.1 07/10] drm/amdgpu: Allow P2P access through XGMI

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Message-ID: <CADnq5_NacNmcKKQUdrbTtEGAn8UCvvJHki+JMUPMRA2AB6T8VA@mail.gmail.com>
Date: Wed, 30 Apr 2025 08:57:30 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Felix Kuehling <felix.kuehling@....com>, Hao Zhou <hao.zhou@....com>, 
	Christian König <christian.koenig@....com>, 
	Alex Deucher <alexander.deucher@....com>, airlied@...il.com, simona@...ll.ch, 
	Yunxiang.Li@....com, matthew.auld@...el.com, tvrtko.ursulin@...lia.com, 
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH AUTOSEL 6.1 07/10] drm/amdgpu: Allow P2P access through XGMI

On Tue, Apr 29, 2025 at 8:03 PM Sasha Levin <sashal@...nel.org> wrote:
>
> From: Felix Kuehling <felix.kuehling@....com>
>
> [ Upstream commit a92741e72f91b904c1d8c3d409ed8dbe9c1f2b26 ]
>
> If peer memory is accessible through XGMI, allow leaving it in VRAM
> rather than forcing its migration to GTT on DMABuf attachment.
>
> Signed-off-by: Felix Kuehling <felix.kuehling@....com>
> Tested-by: Hao (Claire) Zhou <hao.zhou@....com>
> Reviewed-by: Christian König <christian.koenig@....com>
> Signed-off-by: Alex Deucher <alexander.deucher@....com>
> (cherry picked from commit 372c8d72c3680fdea3fbb2d6b089f76b4a6d596a)
> Signed-off-by: Sasha Levin <sashal@...nel.org>

This patch is only applicable to 6.15 and newer.  Please drop for stable.

Alex

> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 30 ++++++++++++++++++++-
>  1 file changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> index ab06cb4d7b358..4dcc7de961d08 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> @@ -42,6 +42,29 @@
>  #include <linux/pci-p2pdma.h>
>  #include <linux/pm_runtime.h>
>
> +static const struct dma_buf_attach_ops amdgpu_dma_buf_attach_ops;
> +
> +/**
> + * dma_buf_attach_adev - Helper to get adev of an attachment
> + *
> + * @attach: attachment
> + *
> + * Returns:
> + * A struct amdgpu_device * if the attaching device is an amdgpu device or
> + * partition, NULL otherwise.
> + */
> +static struct amdgpu_device *dma_buf_attach_adev(struct dma_buf_attachment *attach)
> +{
> +       if (attach->importer_ops == &amdgpu_dma_buf_attach_ops) {
> +               struct drm_gem_object *obj = attach->importer_priv;
> +               struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
> +
> +               return amdgpu_ttm_adev(bo->tbo.bdev);
> +       }
> +
> +       return NULL;
> +}
> +
>  /**
>   * amdgpu_dma_buf_attach - &dma_buf_ops.attach implementation
>   *
> @@ -53,12 +76,14 @@
>  static int amdgpu_dma_buf_attach(struct dma_buf *dmabuf,
>                                  struct dma_buf_attachment *attach)
>  {
> +       struct amdgpu_device *attach_adev = dma_buf_attach_adev(attach);
>         struct drm_gem_object *obj = dmabuf->priv;
>         struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
>         struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
>         int r;
>
> -       if (pci_p2pdma_distance(adev->pdev, attach->dev, false) < 0)
> +       if (!amdgpu_dmabuf_is_xgmi_accessible(attach_adev, bo) &&
> +           pci_p2pdma_distance(adev->pdev, attach->dev, false) < 0)
>                 attach->peer2peer = false;
>
>         r = pm_runtime_get_sync(adev_to_drm(adev)->dev);
> @@ -479,6 +504,9 @@ bool amdgpu_dmabuf_is_xgmi_accessible(struct amdgpu_device *adev,
>         struct drm_gem_object *obj = &bo->tbo.base;
>         struct drm_gem_object *gobj;
>
> +       if (!adev)
> +               return false;
> +
>         if (obj->import_attach) {
>                 struct dma_buf *dma_buf = obj->import_attach->dmabuf;
>
> --
> 2.39.5
>