linux-kernel - Re: [PATCH] virtio_mem: prevent overflow with subblock size

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Message-ID: <201e8ab5-ec50-af86-0ffc-d25befdba14e@redhat.com>
Date:   Mon, 8 Jun 2020 09:34:51 +0200
From:   David Hildenbrand <david@...hat.com>
To:     teawater <teawaterz@...ux.alibaba.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jason Wang <jasowang@...hat.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio_mem: prevent overflow with subblock size

On 08.06.20 09:12, teawater wrote:
> 
> 
>> 2020年6月8日 14:58，David Hildenbrand <david@...hat.com> 写道：
>>
>> On 08.06.20 08:14, Michael S. Tsirkin wrote:
>>> If subblock size is large (e.g. 1G) 32 bit math involving it
>>> can overflow. Rather than try to catch all instances of that,
>>> let's tweak block size to 64 bit.
>>
>> I fail to see where we could actually trigger an overflow. The reported
>> warning looked like a false positive to me.
>>
>>>
>>> It ripples through UAPI which is an ABI change, but it's not too late to
>>> make it, and it will allow supporting >4Gbyte blocks while might
>>> become necessary down the road.
>>>
>>
>> This might break cloud-hypervisor, who's already implementing this
>> protocol upstream (ccing Hui).
>> https://github.com/cloud-hypervisor/cloud-hypervisor/blob/master/vm-virtio/src/mem.rs
>>
>> (blocks in the gigabyte range were never the original intention of
>> virtio-mem, but I am not completely opposed to that)
> 
> If you think virtio_mem need this patch, I think cloud-hypervisor should follow this update (I will post PR for it).

Thanks Hui. So we can still do last-minute changes if we all agree it
makes sense.

@MST can you rephrase the patch description to highlight that this is a
preparation for the future only and not actually currently broken?
"virtio-mem: convert device block size into 64bit" ...

With that

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb