Re: [PATCH v1 6/7] virtio-mem: use page_offline_(start|end) when setting PageOffline()

[Mike Rapoport]

On Thu, Apr 29, 2021 at 02:25:18PM +0200, David Hildenbrand wrote:
> Let's properly use page_offline_(start|end) to synchronize setting
> PageOffline(), so we won't have valid page access to unplugged memory
> regions from /proc/kcore.
> 
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  drivers/virtio/virtio_mem.c | 2 ++
>  mm/util.c                   | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index 10ec60d81e84..dc2a2e2b2ff8 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -1065,6 +1065,7 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
>  static void virtio_mem_set_fake_offline(unsigned long pfn,
>  					unsigned long nr_pages, bool onlined)
>  {
> +	page_offline_begin();
>  	for (; nr_pages--; pfn++) {
>  		struct page *page = pfn_to_page(pfn);
>  
> @@ -1075,6 +1076,7 @@ static void virtio_mem_set_fake_offline(unsigned long pfn,
>  			ClearPageReserved(page);
>  		}
>  	}
> +	page_offline_end();

I'm not really familiar with ballooning and memory hotplug, but is it the
only place that needs page_offline_{begin,end} ?

>  }
>  
>  /*
> diff --git a/mm/util.c b/mm/util.c
> index 95395d4e4209..d0e357bd65e6 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1046,8 +1046,10 @@ void page_offline_begin(void)
>  {
>  	down_write(&page_offline_rwsem);
>  }
> +EXPORT_SYMBOL(page_offline_begin);

Should have been a part of the previous patch.
  
>  void page_offline_end(void)
>  {
>  	up_write(&page_offline_rwsem);
>  }
> +EXPORT_SYMBOL(page_offline_end);

Ditto

> -- 
> 2.30.2
> 

-- 
Sincerely yours,
Mike.