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

[zhenwei pi <pizhenwei@bytedance.com>]

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