On 25.05.22 01:32, zhenwei pi wrote:
>
>
> On 5/25/22 03:35, Sean Christopherson wrote:
>> On Fri, May 20, 2022, zhenwei pi wrote:
>>> @@ -59,6 +60,12 @@ enum virtio_balloon_config_read {
>>> VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0,
>>> };
>>>
>>> +/* the request body to commucate with host side */
>>> +struct __virtio_balloon_recover {
>>> + struct virtio_balloon_recover vbr;
>>> + __virtio32 pfns[VIRTIO_BALLOON_PAGES_PER_PAGE];
>>
>> I assume this is copied from virtio_balloon.pfns, which also uses
>> __virtio32, but
>> isn't that horribly broken? PFNs are 'unsigned long', i.e. 64 bits on
>> 64-bit kernels.
>> x86-64 at least most definitely generates 64-bit PFNs. Unless there's magic
>> I'm
>> missing, page_to_balloon_pfn() will truncate PFNs and feed the host bad info.
>>
>
> Yes, I also noticed this point, I suppose the balloon device can not
> work on a virtual machine which has physical address larger than 16T.
Yes, that's a historical artifact and we never ran into it in practice
-- because 16TB VMs are still rare, especially when paired with
virtio-balloon inflation/deflation. Most probably the guest should just
stop inflating when hitting such a big PFN. In the future, we might want
a proper sg interface instead.
--
Thanks,
David / dhildenb
