linux-kernel - RE: [PATCH 1/2] Revert "udmabuf: fix vmap

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Message-ID: <IA0PR11MB71852A481E8A99C9380C7317F8BB2@IA0PR11MB7185.namprd11.prod.outlook.com>
Date: Tue, 22 Apr 2025 05:14:43 +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>, Andrew Morton <akpm@...ux-foundation.org>, Dave Airlie
	<airlied@...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>, Bingbu Cao
	<bingbu.cao@...ux.intel.com>
Subject: RE: [PATCH 1/2] Revert "udmabuf: fix vmap_udmabuf error page set"

Hi Huan,

> Subject: [PATCH 1/2] Revert "udmabuf: fix vmap_udmabuf error page set"
> 
> This reverts commit 18d7de823b7150344d242c3677e65d68c5271b04.
> 
> This given a misuse of vmap_pfn, vmap_pfn only allow none-page based
> user invoke, i.e. PCIe BARs and other.
The commit message can be improved a little bit to briefly explain why vmap_pfn()
would not work for this use-case.

Acked-by: Vivek Kasireddy <vivek.kasireddy@...el.com>

Thanks,
Vivek

> 
> Signed-off-by: Huan Yang <link@...o.com>
> Reported-by: Bingbu Cao <bingbu.cao@...ux.intel.com>
> Closes: https://lore.kernel.org/dri-devel/eb7e0137-3508-4287-98c4-
> 816c5fd98e10@...o.com/T/#mbda4f64a3532b32e061f4e8763bc8e307bea3ca
> 8
> ---
>  drivers/dma-buf/Kconfig   |  1 -
>  drivers/dma-buf/udmabuf.c | 22 +++++++---------------
>  2 files changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index fee04fdb0822..b46eb8a552d7 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -36,7 +36,6 @@ 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 7eee3eb47a8e..79845565089d 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -109,29 +109,21 @@ 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;
> -	unsigned long *pfns;
> +	struct page **pages;
>  	void *vaddr;
>  	pgoff_t pg;
> 
>  	dma_resv_assert_held(buf->resv);
> 
> -	/**
> -	 * 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)
> +	pages = kvmalloc_array(ubuf->pagecount, sizeof(*pages),
> GFP_KERNEL);
> +	if (!pages)
>  		return -ENOMEM;
> 
> -	for (pg = 0; pg < ubuf->pagecount; pg++) {
> -		unsigned long pfn = folio_pfn(ubuf->folios[pg]);
> -
> -		pfn += ubuf->offsets[pg] >> PAGE_SHIFT;
> -		pfns[pg] = pfn;
> -	}
> +	for (pg = 0; pg < ubuf->pagecount; pg++)
> +		pages[pg] = &ubuf->folios[pg]->page;
> 
> -	vaddr = vmap_pfn(pfns, ubuf->pagecount, PAGE_KERNEL);
> -	kvfree(pfns);
> +	vaddr = vm_map_ram(pages, ubuf->pagecount, -1);
> +	kvfree(pages);
>  	if (!vaddr)
>  		return -EINVAL;
> 
> --
> 2.48.1