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SubjectRe: Re: [PATCH 3/3] virtio_balloon: Introduce memory recover
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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.

I still let the recover VQ keep aligned with the inflate VQ and deflate
VQ. I prefer the recover VQ to be workable/unworkable with
inflate/deflate VQ together. So I leave this to the virtio balloon
maintainer to decide ...

>> @@ -494,6 +511,198 @@ static void update_balloon_size_func(struct work_struct *work)
>> queue_work(system_freezable_wq, work);
>> }
>>
>> +/*
>> + * virtballoon_memory_failure - notified by memory failure, try to fix the
>> + * corrupted page.
>> + * The memory failure notifier is designed to call back when the kernel handled
>> + * successfully only, WARN_ON_ONCE on the unlikely condition to find out any
>> + * error(memory error handling is a best effort, not 100% coverd).
>> + */
>> +static int virtballoon_memory_failure(struct notifier_block *notifier,
>> + unsigned long pfn, void *parm)
>> +{
>> + struct virtio_balloon *vb = container_of(notifier, struct virtio_balloon,
>> + memory_failure_nb);
>> + struct page *page;
>> + struct __virtio_balloon_recover *out_vbr;
>> + struct scatterlist sg;
>> + unsigned long flags;
>> + int err;
>> +
>> + page = pfn_to_online_page(pfn);
>> + if (WARN_ON_ONCE(!page))
>> + return NOTIFY_DONE;
>> +
>> + if (PageHuge(page))
>> + return NOTIFY_DONE;
>> +
>> + if (WARN_ON_ONCE(!PageHWPoison(page)))
>> + return NOTIFY_DONE;
>> +
>> + if (WARN_ON_ONCE(page_count(page) != 1))
>> + return NOTIFY_DONE;
>> +
>> + get_page(page); /* balloon reference */
>> +
>> + out_vbr = kzalloc(sizeof(*out_vbr), GFP_KERNEL);
>> + if (WARN_ON_ONCE(!out_vbr))
>> + return NOTIFY_BAD;
>
> Not that it truly matters, but won't failure at this point leak the poisoned page?

I'll fix this, thanks!

--
zhenwei pi

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