linux-kernel - Re: [PATCH v3 2/9] arch/arm/mm/dma-mapping.c: Convert to use vm_insert

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Date:   Mon, 10 Dec 2018 16:32:06 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Souptick Joarder <jrdr.linux@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        iamjoonsoo.kim@....com, treding@...dia.com,
        Kees Cook <keescook@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 2/9] arch/arm/mm/dma-mapping.c: Convert to use
 vm_insert_range

On 08/12/2018 20:01, Souptick Joarder wrote:
> Hi Robin,
> 
> On Fri, Dec 7, 2018 at 12:07 AM Souptick Joarder <jrdr.linux@...il.com> wrote:
>>
>> Convert to use vm_insert_range() to map range of kernel
>> memory to user vma.
>>
>> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
>> ---
>>   arch/arm/mm/dma-mapping.c | 21 +++++++--------------
>>   1 file changed, 7 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
>> index 661fe48..4eec323 100644
>> --- a/arch/arm/mm/dma-mapping.c
>> +++ b/arch/arm/mm/dma-mapping.c
>> @@ -1582,31 +1582,24 @@ static int __arm_iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma
>>                      void *cpu_addr, dma_addr_t dma_addr, size_t size,
>>                      unsigned long attrs)
>>   {
>> -       unsigned long uaddr = vma->vm_start;
>> -       unsigned long usize = vma->vm_end - vma->vm_start;
>> +       unsigned long page_count = vma_pages(vma);
>>          struct page **pages = __iommu_get_pages(cpu_addr, attrs);
>>          unsigned long nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
>>          unsigned long off = vma->vm_pgoff;
>> +       int err;
>>
>>          if (!pages)
>>                  return -ENXIO;
>>
>> -       if (off >= nr_pages || (usize >> PAGE_SHIFT) > nr_pages - off)
>> +       if (off >= nr_pages || page_count > nr_pages - off)
>>                  return -ENXIO;
>>
>>          pages += off;
>> +       err = vm_insert_range(vma, vma->vm_start, pages, page_count);
> 
> Just to clarify, do we need to adjust page_count with vma->vm_pgoff as
> original code
> have not consider it and run the loop for entire range irrespective of
> vma->vm_pgoff value ?

In this instance, page_count is the size of the VMA, not the size of the 
pages array itself, so as I understand things this patch is true to the 
original code as-is.

Robin.

> 
>> +       if (err)
>> +               pr_err("Remapping memory failed: %d\n", err);
>>
>> -       do {
>> -               int ret = vm_insert_page(vma, uaddr, *pages++);
>> -               if (ret) {
>> -                       pr_err("Remapping memory failed: %d\n", ret);
>> -                       return ret;
>> -               }
>> -               uaddr += PAGE_SIZE;
>> -               usize -= PAGE_SIZE;
>> -       } while (usize > 0);
>> -
>> -       return 0;
>> +       return err;
>>   }
>>   static int arm_iommu_mmap_attrs(struct device *dev,
>>                  struct vm_area_struct *vma, void *cpu_addr,
>> --
>> 1.9.1
>>