linux-kernel - RE: [PATCH v6 3/7] udmabuf: fix vmap

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Message-ID: <IA0PR11MB718549B45FCA4C85C1C99CA4F8642@IA0PR11MB7185.namprd11.prod.outlook.com>
Date: Thu, 12 Sep 2024 22:37:57 +0000
From: "Kasireddy, Vivek" <vivek.kasireddy@...el.com>
To: Huan Yang <link@...o.com>, Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>, Gerd Hoffmann
	<kraxel@...hat.com>, "linux-media@...r.kernel.org"
	<linux-media@...r.kernel.org>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.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 v6 3/7] udmabuf: fix vmap_udmabuf error page set

Hi Huan,

> Subject: [PATCH v6 3/7] udmabuf: fix vmap_udmabuf error page set
> 
> 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.
> 
> By this, we removed page usage in udmabuf totally.
> 
I think this would probably need a Fixes tag:
Fixes: 5e72b2b41a21 ("udmabuf: convert udmabuf driver to use folios")

Thanks,
Vivek

> Suggested-by: Vivek Kasireddy <vivek.kasireddy@...el.com>
> Signed-off-by: Huan Yang <link@...o.com>
> Acked-by: Vivek Kasireddy <vivek.kasireddy@...el.com>
> ---
>  drivers/dma-buf/Kconfig   |  1 +
>  drivers/dma-buf/udmabuf.c | 22 +++++++++++++++-------
>  2 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index b46eb8a552d7..fee04fdb0822 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -36,6 +36,7 @@ config UDMABUF
>  	depends on DMA_SHARED_BUFFER
>  	depends on MEMFD_CREATE || COMPILE_TEST
>  	depends on MMU
> +	select VMAP_PFN
>  	help
>  	  A driver to let userspace turn memfd regions into dma-bufs.
>  	  Qemu can use this to create host dmabufs for guest framebuffers.
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index ba9dbc7caf71..aa182a9dcdfa 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -103,21 +103,29 @@ 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;
>  	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);
> +	kvfree(pfns);
>  	if (!vaddr)
>  		return -EINVAL;
> 
> --
> 2.45.2