Re: [Xen-devel] question about memory allocation for driver domain

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 09/02/2015 20:02, Oleksandr Tyshchenko wrote:
> On Mon, Feb 9, 2015 at 10:31 AM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> > On 07/02/2015 01:15, Oleksandr Tyshchenko wrote:
> Hi Julien
Hi Oleksandr,

> > > On Thu, Feb 5, 2015 at 6:36 PM, Oleksandr Tyshchenko
> > The next problem is ballooning. When the guest balloon out memory, the page
> > will be freed by Xen and can be re-used by another domain.
> >
> > When guest balloon in, Xen will allocate a page (randomly) and therefore the
> > mapping won't be anymore IPA (guest physical address) == PA (physical
> > address). Any DMA request using this address will read/write data from wrong
> > memory.
> Is it possible to disable ballon driver for domd?
I think updating is_domain_direct_mapped is enough here.

We won't support memory hotplug for this kind of domain.

> > The last problem but not the least is, depending on which backend you are
> > running in the 1:1 domain (such blkback), grant won't be mapped 1:1 to the
> > guest, so you will have to use swiotlb in order to use the right DMA
> > address. For instance, without swiotlb, guest won't be able to use a disk
> > partition via blkfront. This because the backend is giving directly the
> > grant address to the block driver. To solve this, we have to use swiotlb and
> > set specific DMA callback. For now, there are only used for DOM0.
> We are using SWIOTLB for domd too.
Good :).


Regards,

--
Julien Grall

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