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

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Date:   Thu, 1 Jun 2017 13:50:44 +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 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.

Cheers,

-- 
Julien Grall