linux-kernel - RE: [PATCH v3 3/5] fix vmap

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Message-ID: <IA0PR11MB7185465DDE79BC8DD84B8BE1F8822@IA0PR11MB7185.namprd11.prod.outlook.com>
Date: Sat, 17 Aug 2024 00:54:26 +0000
From: "Kasireddy, Vivek" <vivek.kasireddy@...el.com>
To: Huan Yang <link@...o.com>, Gerd Hoffmann <kraxel@...hat.com>, Sumit Semwal
	<sumit.semwal@...aro.org>, Christian König
	<christian.koenig@....com>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "linux-media@...r.kernel.org"
	<linux-media@...r.kernel.org>, "linaro-mm-sig@...ts.linaro.org"
	<linaro-mm-sig@...ts.linaro.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "opensource.kernel@...o.com" <opensource.kernel@...o.com>
Subject: RE: [PATCH v3 3/5] fix vmap_udmabuf error page set

Hi Huan,

> Subject: [PATCH v3 3/5] fix vmap_udmabuf error page set
Please prepend a "udmabuf:" to the subject line and improve the wording.

> 
> Currently vmap_udmabuf set page's array by each folio.
> But, ubuf->folios is only contain's the folio's head page.
> 
> That mean we repeatedly mapped the folio head page to the vmalloc area.
> 
> Due to udmabuf can use hugetlb, if HVO enabled, tail page may not exist,
> so, we can't use page array to map, instead, use pfn array.
> 
> Signed-off-by: Huan Yang <link@...o.com>
> Suggested-by: Vivek Kasireddy <vivek.kasireddy@...el.com>
> ---
>  drivers/dma-buf/udmabuf.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 3ec72d47bb1c..4ec54c60d76c 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -67,21 +67,29 @@ static int mmap_udmabuf(struct dma_buf *buf,
> struct vm_area_struct *vma)
>  static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
>  {
>  	struct udmabuf *ubuf = buf->priv;
> -	struct page **pages;
> +	unsigned long *pfns;

I wish there was a way to easily test the vmap scenario but its great that
you are able to eliminate the usage of "struct page" completely from
udmabuf driver, with this patch. 

>  	void *vaddr;
>  	pgoff_t pg;
> 
>  	dma_resv_assert_held(buf->resv);
> 
> -	pages = kvmalloc_array(ubuf->pagecount, sizeof(*pages),
> GFP_KERNEL);
> -	if (!pages)
> +	/**
> +	 * HVO may free tail pages, so just use pfn to map each folio
> +	 * into vmalloc area.
> +	 */
> +	pfns = kvmalloc_array(ubuf->pagecount, sizeof(*pfns), GFP_KERNEL);
> +	if (!pfns)
>  		return -ENOMEM;
> 
> -	for (pg = 0; pg < ubuf->pagecount; pg++)
> -		pages[pg] = &ubuf->folios[pg]->page;
> +	for (pg = 0; pg < ubuf->pagecount; pg++) {
> +		unsigned long pfn = folio_pfn(ubuf->folios[pg]);
> 
> -	vaddr = vm_map_ram(pages, ubuf->pagecount, -1);
> -	kvfree(pages);
> +		pfn += ubuf->offsets[pg] >> PAGE_SHIFT;
> +		pfns[pg] = pfn;
> +	}
> +
> +	vaddr = vmap_pfn(pfns, ubuf->pagecount, PAGE_KERNEL);
Looks like this would require a "select VMAP_PFN" in Kconfig.

Thanks,
Vivek

> +	kvfree(pfns);
>  	if (!vaddr)
>  		return -EINVAL;
> 
> --
> 2.45.2