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

[zhenwei pi]

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