| Message ID | 20210429122519.15183-7-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages | expand |
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@redhat.com> > --- > 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 >
On 02.05.21 08:33, Mike Rapoport wrote: > 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@redhat.com> >> --- >> 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} ? Existing balloon implementations that I am aware of (Hyper-V, XEN, virtio-balloon, vmware-balloon) usually allow reading inflated memory; doing so might result in unnecessary overhead in the hypervisor, so we really want to avoid it -- but it's strictly not forbidden and has been working forever. So we barely care about races: if there would be a rare race, we'd still be able to read that memory. For virtio-mem, it'll be different in the future when using shmem, huge pages, !anonymous private mappings, ... as backing storage for a VM; there will be a virtio spec extension to document that virtio-mem changes that indicate the new behavior won't allow reading unplugged memory and doing so will result in undefined behavior.
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@redhat.com> the patch looks good to me as such Acked-by: Michael S. Tsirkin <mst@redhat.com> Feel free to merge with rest of patcgset - it seems to mostly live in the fs/mm space. IF you respin, maybe add the explanation you sent in response to Mike's comments in the commit log. > --- > 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(); > } > > /* > 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); > > void page_offline_end(void) > { > up_write(&page_offline_rwsem); > } > +EXPORT_SYMBOL(page_offline_end); > -- > 2.30.2
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(); } /* 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); void page_offline_end(void) { up_write(&page_offline_rwsem); } +EXPORT_SYMBOL(page_offline_end);
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@redhat.com> --- drivers/virtio/virtio_mem.c | 2 ++ mm/util.c | 2 ++ 2 files changed, 4 insertions(+)