Re: [PATCH] virtio-balloon spec: provide a version of the "silent deflate" feature that works

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
> On Fri, Sep 07, 2012 at 04:09:50PM +0930, Rusty Russell wrote:
>> > So it looks like a bug: we should teach driver to tell host first on leak?
>> > Yan, Vadim, can you comment please?
>> >
>> > Also if true, looks like this bit will be useful to detect a fixed driver on
>> > the hypervisor side - to avoid unmapping such pages? Rusty what do you
>> > think?
>> 
>> So, feature is unimplemented in qemu, and broken in drivers.  I starting
>> to share Paolo's dislike of it.
>
> What is broken in drivers?

Because supporting the feature is *not* optional for a driver.

If the device said MUST_TELL_HOST, it meant that the driver *had* to
tell the host before it touched the page, otherwise Bad Things might
happen.  It was in the original spec precisely to allow devices to
actually *remove* pages.

Noone ever noticed the windows driver didn't support it, because qemu
never requires MUST_TELL_HOST.

So in practice, it's now an optional feature.  Since no device used it
anyway, we're better off discarding it than trying to fix it.

If someone wants an *optional* "tell me first" feature later, that's
easy to add, but I don't see why they'd want to.

> Do we really know there are no hypervisors implementing it?

As much as can be known.  Qemu doesn't, lkvm doesn't.

> As I said above drivers do have support.

Not the windows drivers.  So it's optional, thus removing it will likely
harm noone.

Cheers,
Rusty.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux