Messages in this thread Patch in this message | | | Date | Mon, 20 Nov 2017 19:42:40 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v17 6/6] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ |
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On 11/14/2017 01:32 AM, Michael S. Tsirkin wrote: > You should Cc Nitesh who is working on a related feature.
OK, I'll do. We have two more issues which haven't been discussed yet, please have a check below.
> > On Mon, Nov 13, 2017 at 06:34:48PM +0800, Wei Wang wrote: >> Ping for comments, thanks. >> >> On 11/03/2017 04:13 PM, Wei Wang wrote: >>> +static void virtballoon_cmd_report_free_page_start(struct virtio_balloon *vb) >>> +{ >>> + unsigned long flags; >>> + >>> + vb->report_free_page_stop = false; > this flag is used a lot outside any locks. Why is this safe? > Please add some comments explaining access to this flag.
I will revert the logic as suggested: vb->report_free_page. Also plan to simplify its usage as below.
The flag is set or cleared in the config handler according to the new_cmd_id given by the host:
new_cmd_id=0: WRITE_ONCE(vb->report_free_page, false); // stop reporting new_cmd_id != old_cmd_id: WRITE_ONCE(vb->report_free_page, true); // start reporting
The flag is read by virtio_balloon_send_free_pages() - the callback to report free pages:
if (!READ_ONCE(vb->report_free_page)) return false;
I don't find where it could be unsafe then (the flag is written by the config handler only).
> >>> +} >>> + >>> static inline s64 towards_target(struct virtio_balloon *vb) >>> { >>> s64 target; >>> @@ -597,42 +673,147 @@ static void update_balloon_size_func(struct work_struct *work) >>> queue_work(system_freezable_wq, work); >>> } >>> -static int init_vqs(struct virtio_balloon *vb) >>> +static bool virtio_balloon_send_free_pages(void *opaque, unsigned long pfn, >>> + unsigned long nr_pages) >>> { >>> - struct virtqueue *vqs[3]; >>> - vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request }; >>> - static const char * const names[] = { "inflate", "deflate", "stats" }; >>> - int err, nvqs; >>> + struct virtio_balloon *vb = (struct virtio_balloon *)opaque; >>> + void *addr = (void *)pfn_to_kaddr(pfn); > How do we know all free pages have a kaddr?
For x86_64, it works well since the kernel has all the physical memory mapped already. But for 32-bit kernel, yes, the high memory usually isn't mapped and thus no kaddr. Essentially, this pfn_to_kaddr convert isn't necessary, we do it here because the current API that virtio has is based on "struct scatterlist", which takes a kaddr, and this kaddr is then convert back to physical address in virtqueue_add() when assigning to desc->addr.
I think a better solution would be to add a new API, which directly assigns the caller's guest physical address to desc->addr, similar to the previous implementation "add_one_chunk()" (https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg02452.html). But we can change that to a general virtio API: virtqueue_add_one_desc(struct virtqueue *_vq, u64 base_addr, u32 size, bool in_desc, void *data);
What do you think?
Best, Wei
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