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Subject: Re: [PATCH V2 2/7] xen/grants: support allocating consecutive grants
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc:     Stefano Stabellini <sstabellini@kernel.org>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Juergen Gross <jgross@suse.com>, Julien Grall <julien@xen.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Christoph Hellwig <hch@infradead.org>
References: <1651947548-4055-1-git-send-email-olekstysh@gmail.com>
 <1651947548-4055-3-git-send-email-olekstysh@gmail.com>
 <8409e636-94e3-e231-f181-c76a849534a1@gmail.com>
 <24748b59-e2ed-1d7d-801e-ab9dc12b0983@oracle.com>
From:   Oleksandr <olekstysh@gmail.com>
Message-ID: <749e79d0-c920-adee-c145-edc4153a99f9@gmail.com>
Date:   Thu, 12 May 2022 09:11:49 +0300
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On 12.05.22 00:09, Boris Ostrovsky wrote:


Hello Boris


>
> On 5/11/22 2:00 PM, Oleksandr wrote:
>>
>> On 07.05.22 21:19, Oleksandr Tyshchenko wrote:
>>
>> Hello Boris, Stefano
>>
>>
>>> From: Juergen Gross <jgross@suse.com>
>>>
>>> For support of virtio via grant mappings in rare cases larger mappings
>>> using consecutive grants are needed. Support those by adding a bitmap
>>> of free grants.
>>>
>>> As consecutive grants will be needed only in very rare cases (e.g. when
>>> configuring a virtio device with a multi-page ring), optimize for the
>>> normal case of non-consecutive allocations.
>>>
>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>> ---
>>> Changes RFC -> V1:
>>>     - no changes
>>>     Changes V1 -> V2:
>>>     - no changes
>>
>>
>> May I please ask for the review here?
>
>
>
> I had a quick look but I am stuck on get_free_seq(), I need to stare 
> at it some more. Unless someone else reviews this, I will try to get 
> to this in the next couple of days.


Thank you!


>
>
>
> One thing I did notice is
>
>
>>
>>> @@ -1452,6 +1624,13 @@ int gnttab_init(void)
>>>           }
>>>       }
>>>   +    i = gnttab_interface->grefs_per_grant_frame * 
>>> max_nr_grant_frames;
>>> +    gnttab_free_bitmap = bitmap_zalloc(i, GFP_KERNEL);
>>> +    if (!gnttab_free_bitmap) {
>>> +        ret = -ENOMEM;
>>> +        goto ini_nomem;
>>> +    }
>
>
> This overwrites 'i' and will break error handling at ini_nomem.


Indeed, will fix. Thank you for pointing this out.


>
>
> -boris
>
>
-- 
Regards,

Oleksandr Tyshchenko