linux-kernel - Re: [PATCH 8/9] xen/gntdev.c: Convert to use vm_insert

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Date:   Tue, 15 Jan 2019 10:29:17 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Juergen Gross <jgross@...e.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        robin.murphy@....com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 8/9] xen/gntdev.c: Convert to use vm_insert_range

On 1/14/19 11:49 PM, Souptick Joarder wrote:
> On Tue, Jan 15, 2019 at 4:58 AM Boris Ostrovsky
> <boris.ostrovsky@...cle.com> wrote:
>> On 1/11/19 10:12 AM, Souptick Joarder 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>
>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>>
>> (although it would be good to mention in the commit that you are also
>> replacing count with vma_pages(vma), and why)
> The original code was using count ( *count = vma_pages(vma)* )
> which is same as this patch. Do I need capture it change log ?


I'd just say that because theoretically count might not be equal to
map->count we should use the latter as input to vm_insert_range().

Thanks.
-boris



>
>>
>>> ---
>>>  drivers/xen/gntdev.c | 16 ++++++----------
>>>  1 file changed, 6 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
>>> index b0b02a5..ca4acee 100644
>>> --- a/drivers/xen/gntdev.c
>>> +++ b/drivers/xen/gntdev.c
>>> @@ -1082,18 +1082,17 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>>  {
>>>       struct gntdev_priv *priv = flip->private_data;
>>>       int index = vma->vm_pgoff;
>>> -     int count = vma_pages(vma);
>>>       struct gntdev_grant_map *map;
>>> -     int i, err = -EINVAL;
>>> +     int err = -EINVAL;
>>>
>>>       if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
>>>               return -EINVAL;
>>>
>>>       pr_debug("map %d+%d at %lx (pgoff %lx)\n",
>>> -                     index, count, vma->vm_start, vma->vm_pgoff);
>>> +                     index, vma_pages(vma), vma->vm_start, vma->vm_pgoff);
>>>
>>>       mutex_lock(&priv->lock);
>>> -     map = gntdev_find_map_index(priv, index, count);
>>> +     map = gntdev_find_map_index(priv, index, vma_pages(vma));
>>>       if (!map)
>>>               goto unlock_out;
>>>       if (use_ptemod && map->vma)
>>> @@ -1145,12 +1144,9 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>>               goto out_put_map;
>>>
>>>       if (!use_ptemod) {
>>> -             for (i = 0; i < count; i++) {
>>> -                     err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
>>> -                             map->pages[i]);
>>> -                     if (err)
>>> -                             goto out_put_map;
>>> -             }
>>> +             err = vm_insert_range(vma, map->pages, map->count);
>>> +             if (err)
>>> +                     goto out_put_map;
>>>       } else {
>>>  #ifdef CONFIG_X86
>>>               /*