linux-kernel - Re: [PATCH v2] dma-mapping: use vmalloc_to

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Message-ID: <CADu_u-OYA+Z_y-DBLxyUYGhmLVMtLggmZ_SnRiEtw9EGrO4oGg@mail.gmail.com>
Date:   Fri, 16 Jul 2021 15:53:41 +0300
From:   Roman Skakun <rm.skakun@...il.com>
To:     Christoph Hellwig <hch@....de>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        xen-devel@...ts.xenproject.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Volodymyr Babchuk <volodymyr_babchuk@...m.com>,
        Andrii Anisov <andrii_anisov@...m.com>,
        Roman Skakun <Roman_Skakun@...m.com>,
        Roman Skakun <rm.skakun@...il.com>
Subject: Re: [PATCH v2] dma-mapping: use vmalloc_to_page for vmalloc addresses

> Technically this looks good.  But given that exposing a helper
> that does either vmalloc_to_page or virt_to_page is one of the
> never ending MM discussions I don't want to get into that discussion
> and just keep it local in the DMA code.
>
> Are you fine with me applying this version?

Looks good to me, thanks!
But, Stefano asked me about using created helper in the
xen_swiotlb_free_coherent()
and I created a patch according to this mention.

We can merge this patch and create a new one for
xen_swiotlb_free_coherent() later.

пт, 16 июл. 2021 г. в 12:35, Christoph Hellwig <hch@....de>:
>
> Technically this looks good.  But given that exposing a helper
> that does either vmalloc_to_page or virt_to_page is one of the
> never ending MM discussions I don't want to get into that discussion
> and just keep it local in the DMA code.
>
> Are you fine with me applying this version?
>
> ---
> From 40ac971eab89330d6153e7721e88acd2d98833f9 Mon Sep 17 00:00:00 2001
> From: Roman Skakun <Roman_Skakun@...m.com>
> Date: Fri, 16 Jul 2021 11:39:34 +0300
> Subject: dma-mapping: handle vmalloc addresses in
>  dma_common_{mmap,get_sgtable}
>
> xen-swiotlb can use vmalloc backed addresses for dma coherent allocations
> and uses the common helpers.  Properly handle them to unbreak Xen on
> ARM platforms.
>
> Fixes: 1b65c4e5a9af ("swiotlb-xen: use xen_alloc/free_coherent_pages")
> Signed-off-by: Roman Skakun <roman_skakun@...m.com>
> Reviewed-by: Andrii Anisov <andrii_anisov@...m.com>
> [hch: split the patch, renamed the helpers]
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  kernel/dma/ops_helpers.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/dma/ops_helpers.c b/kernel/dma/ops_helpers.c
> index 910ae69cae77..af4a6ef48ce0 100644
> --- a/kernel/dma/ops_helpers.c
> +++ b/kernel/dma/ops_helpers.c
> @@ -5,6 +5,13 @@
>   */
>  #include <linux/dma-map-ops.h>
>
> +static struct page *dma_common_vaddr_to_page(void *cpu_addr)
> +{
> +       if (is_vmalloc_addr(cpu_addr))
> +               return vmalloc_to_page(cpu_addr);
> +       return virt_to_page(cpu_addr);
> +}
> +
>  /*
>   * Create scatter-list for the already allocated DMA buffer.
>   */
> @@ -12,7 +19,7 @@ int dma_common_get_sgtable(struct device *dev, struct sg_table *sgt,
>                  void *cpu_addr, dma_addr_t dma_addr, size_t size,
>                  unsigned long attrs)
>  {
> -       struct page *page = virt_to_page(cpu_addr);
> +       struct page *page = dma_common_vaddr_to_page(cpu_addr);
>         int ret;
>
>         ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
> @@ -32,6 +39,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
>         unsigned long user_count = vma_pages(vma);
>         unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
>         unsigned long off = vma->vm_pgoff;
> +       struct page *page = dma_common_vaddr_to_page(cpu_addr);
>         int ret = -ENXIO;
>
>         vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, attrs);
> @@ -43,7 +51,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
>                 return -ENXIO;
>
>         return remap_pfn_range(vma, vma->vm_start,
> -                       page_to_pfn(virt_to_page(cpu_addr)) + vma->vm_pgoff,
> +                       page_to_pfn(page) + vma->vm_pgoff,
>                         user_count << PAGE_SHIFT, vma->vm_page_prot);
>  #else
>         return -ENXIO;
> --
> 2.30.2
>


-- 
Best Regards, Roman.