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

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Date:   Wed, 11 May 2022 17:09:33 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Oleksandr <olekstysh@...il.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     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 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.


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.


-boris