linux-kernel - Re: [PATCH] nouveau: fix the start/end range for migration

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Date:   Mon, 31 Aug 2020 08:51:17 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Ralph Campbell <rcampbell@...dia.com>
CC:     <nouveau@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>, Ben Skeggs <bskeggs@...hat.com>
Subject: Re: [PATCH] nouveau: fix the start/end range for migration

On Thu, Aug 27, 2020 at 02:37:44PM -0700, Ralph Campbell wrote:
> The user level OpenCL code shouldn't have to align start and end
> addresses to a page boundary. That is better handled in the nouveau
> driver. The npages field is also redundant since it can be computed
> from the start and end addresses.
> 
> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
> 
> This is for Ben Skegg's nouveau tree.
> 
> I have been working with Karol Herbst on the OpenCL mesa changes for
> nouveau which will be merged upstream soon.
> With or without those changes, the user visible effect of this patch
> only extends the range by one page (round up vs. round down to page
> boundary).
> 
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index 2df1c0460559..888aa0908c5a 100644
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -105,11 +105,14 @@ nouveau_svmm_bind(struct drm_device *dev, void *data,
>  	struct nouveau_cli *cli = nouveau_cli(file_priv);
>  	struct drm_nouveau_svm_bind *args = data;
>  	unsigned target, cmd, priority;
> -	unsigned long addr, end, size;
> +	unsigned long addr, end;
>  	struct mm_struct *mm;
>  
>  	args->va_start &= PAGE_MASK;
> -	args->va_end &= PAGE_MASK;
> +	args->va_end = ALIGN(args->va_end, PAGE_SIZE);
> +	/* If no end address is given, assume a single page. */
> +	if (args->va_end == 0)
> +		args->va_end = args->va_start + PAGE_SIZE;

That is really weird, how is it useful for the kernel to map a region
of unknown size and alignment to the GPU?

Jason