Messages in this thread | | | Date | Mon, 11 Dec 2017 14:38:45 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v18 10/10] virtio-balloon: don't report free pages when page poisoning is enabled |
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On 12/01/2017 11:49 PM, Michael S. Tsirkin wrote: > On Wed, Nov 29, 2017 at 09:55:26PM +0800, Wei Wang wrote: >> The guest free pages should not be discarded by the live migration thread >> when page poisoning is enabled with PAGE_POISONING_NO_SANITY=n, because >> skipping the transfer of such poisoned free pages will trigger false >> positive when new pages are allocated and checked on the destination. >> This patch skips the reporting of free pages in the above case. >> >> Reported-by: Michael S. Tsirkin <mst@redhat.com> >> Signed-off-by: Wei Wang <wei.w.wang@intel.com> >> Cc: Michal Hocko <mhocko@suse.com> >> --- >> drivers/virtio/virtio_balloon.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index 035bd3a..6ac4cff 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -652,7 +652,9 @@ static void report_free_page(struct work_struct *work) >> /* Start by sending the obtained cmd id to the host with an outbuf */ >> send_one_desc(vb, vb->free_page_vq, virt_to_phys(&vb->start_cmd_id), >> sizeof(uint32_t), false, true, false); >> - walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages); >> + if (!(page_poisoning_enabled() && >> + !IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))) >> + walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages); >> /* >> * End by sending the stop id to the host with an outbuf. Use the >> * non-batching mode here to trigger a kick after adding the stop id. > PAGE_POISONING_ZERO is actually OK. > > But I really would prefer it that we still send pages to host, > otherwise debugging becomes much harder. > > And it does not have to be completely useless, even though > you can not discard them as they would be zero-filled then. > > How about a config field telling host what should be there in the free > pages? This way even though host can not discard them, host can send > them out without reading them, still a win. > >
Since this poison value comes with the free page reporting feature, how about sending the poison value via the free_page_vq, along with the cmd id in the outbuf? That is, use the following interface:
struct virtio_balloon_free_page_vq_hdr { bool page_poisoning; __virtio32 poison_value; __virtio32 cmd_id; }
We need "bool page_poisoning" because "poison_value=0" doesn't tell whether page poising is in use by the guest. PAGE_POISONING_ZERO sets "page_poisoning=true, poisoning_value=0", and the host will send the 0-filled pages to the destination (if not sending 0-filled pages, the destination host would offer non-zero pages to the guest) The host can discard free pages only when "page_poisoning=false".
Best, Wei
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