linux-kernel - Re: [PATCH V2 2/7] xen/grants: support allocating consecutive grants

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Date:   Thu, 12 May 2022 09:11:49 +0300
From:   Oleksandr <olekstysh@...il.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Juergen Gross <jgross@...e.com>, Julien Grall <julien@....org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH V2 2/7] xen/grants: support allocating consecutive grants


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@...e.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@...e.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