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

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Message-ID: <0b91491d-8f67-fa22-8b27-7692f00bba51@arm.com>
Date:   Thu, 1 Jun 2017 15:01:09 +0100
From:   Julien Grall <julien.grall@....com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.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

Hi Boris,

On 01/06/17 14:33, Boris Ostrovsky wrote:
> 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.)

Oh. The code in xen_remap_domain_gfn_array is relying on st->va to be 
page aligned. So I think we want to keep PAGE_MASK here.

Cheers,

-- 
Julien Grall