linux-kernel - Re: [PATCH] xen/privcmd: Support correctly 64KB page granularity when mapping memory

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Date:   Thu, 1 Jun 2017 09:33:52 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Julien Grall <julien.grall@....com>, xen-devel@...ts.xen.org
Cc:     sstabellini@...nel.org, jgross@...e.com,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Feng Kan <fkan@....com>
Subject: Re: [PATCH] xen/privcmd: Support correctly 64KB page granularity when
 mapping memory

On 06/01/2017 08:50 AM, Julien Grall wrote:
> Hi Boris,
>
> On 31/05/17 14:54, Boris Ostrovsky wrote:
>> On 05/31/2017 09:03 AM, Julien Grall wrote:
>>> Commit 5995a68 "xen/privcmd: Add support for Linux 64KB page
>>> granularity" did
>>> not go far enough to support 64KB in mmap_batch_fn.
>>>
>>> The variable 'nr' is the number of 4KB chunk to map. However, when
>>> Linux
>>> is using 64KB page granularity the array of pages
>>> (vma->vm_private_data)
>>> contain one page per 64KB. Fix it by incrementing st->index correctly.
>>>
>>> Furthermore, st->va is not correctly incremented as PAGE_SIZE !=
>>> XEN_PAGE_SIZE.
>>>
>>> Fixes: 5995a68 ("xen/privcmd: Add support for Linux 64KB page
>>> granularity")
>>> CC: stable@...r.kernel.org
>>> Reported-by: Feng Kan <fkan@....com>
>>> Signed-off-by: Julien Grall <julien.grall@....com>
>>> ---
>>>  drivers/xen/privcmd.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
>>> index 7a92a5e1d40c..feca75b07fdd 100644
>>> --- a/drivers/xen/privcmd.c
>>> +++ b/drivers/xen/privcmd.c
>>> @@ -362,8 +362,8 @@ static int mmap_batch_fn(void *data, int nr,
>>> void *state)
>>>                  st->global_error = 1;
>>>          }
>>>      }
>>> -    st->va += PAGE_SIZE * nr;
>>> -    st->index += nr;
>>> +    st->va += XEN_PAGE_SIZE * nr;
>>> +    st->index += nr / XEN_PFN_PER_PAGE;
>>>
>>>      return 0;
>>>  }
>>
>>
>> Are we still using PAGE_MASK for xen_remap_domain_gfn_array()?
>
> Do you mean in the xen_xlate_remap_gfn_array implementation? If so
> there are no use of PAGE_MASK as the code has been converted to
> support 64K page granularity.
>
> If you mean the x86 version of xen_remap_domain_gfn_array, then we
> don't really care as x86 only use 4KB page granularity.


I meant right above the change that you made. Should it also be replaced
with XEN_PAGE_MASK? (Sorry for being unclear.)

 ==>     ret = xen_remap_domain_gfn_array(st->vma, st->va & PAGE_MASK,
gfnp, nr,
                                         (int *)gfnp, st->vma->vm_page_prot,
                                         st->domain, cur_pages);

        /* Adjust the global_error? */
        if (ret != nr) {
                if (ret == -ENOENT)
                        st->global_error = -ENOENT;
                else {
                        /* Record that at least one error has happened. */
                        if (st->global_error == 0)
                                st->global_error = 1;
                }
        }
        st->va += PAGE_SIZE * nr;
        st->index += nr;