"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
