diff mbox series

[v2,5/6] virtio-mem: use page_offline_(start|end) when setting PageOffline()

Message ID 20210514172247.176750-6-david@redhat.com (mailing list archive)
State New
Headers show
Series fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages | expand

Commit Message

David Hildenbrand May 14, 2021, 5:22 p.m. UTC
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.

Existing balloon implementations usually allow reading inflated memory;
doing so might result in unnecessary overhead in the hypervisor, which
is currently the case with virtio-mem.

For future virtio-mem use cases, it will be different when using shmem,
huge pages, !anonymous private mappings, ... as backing storage for a VM.
virtio-mem unplugged memory must no longer be accessed and access might
result in undefined behavior. There will be a virtio spec extension to
document this change, including a new feature flag indicating the
changed behavior. We really don't want to race against PFN walkers
reading random page content.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_mem.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Mike Rapoport May 17, 2021, 6:43 a.m. UTC | #1
On Fri, May 14, 2021 at 07:22:46PM +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.
> 
> Existing balloon implementations usually allow reading inflated memory;
> doing so might result in unnecessary overhead in the hypervisor, which
> is currently the case with virtio-mem.
> 
> For future virtio-mem use cases, it will be different when using shmem,
> huge pages, !anonymous private mappings, ... as backing storage for a VM.
> virtio-mem unplugged memory must no longer be accessed and access might
> result in undefined behavior. There will be a virtio spec extension to
> document this change, including a new feature flag indicating the
> changed behavior. We really don't want to race against PFN walkers
> reading random page content.
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>

Acked-by: Mike Rapoport <rppt@linux.ibm.com>

> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  drivers/virtio/virtio_mem.c | 2 ++
>  1 file changed, 2 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();
>  }
>  
>  /*
> -- 
> 2.31.1
> 
>
Oscar Salvador May 25, 2021, 8:20 a.m. UTC | #2
On Fri, May 14, 2021 at 07:22:46PM +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.
> 
> Existing balloon implementations usually allow reading inflated memory;
> doing so might result in unnecessary overhead in the hypervisor, which
> is currently the case with virtio-mem.
> 
> For future virtio-mem use cases, it will be different when using shmem,
> huge pages, !anonymous private mappings, ... as backing storage for a VM.
> virtio-mem unplugged memory must no longer be accessed and access might
> result in undefined behavior. There will be a virtio spec extension to
> document this change, including a new feature flag indicating the
> changed behavior. We really don't want to race against PFN walkers
> reading random page content.
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Oscar Salvador <osalvador@suse.de>
diff mbox series

Patch

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();
 }
 
 /*