Re: Virtio in Xen on Arm (based on IOREQ concept)

[Oleksandr <olekstysh@xxxxxxxxx>]

On 21.07.20 17:27, Julien Grall wrote:
> Hi,
Hello


> On a similar topic, I am a bit surprised you didn't encounter memory 
> exhaustion when trying to use virtio. Because on how Linux currently 
> works (see XSA-300), the backend domain as to have a least as much RAM 
> as the domain it serves. For instance, you have serve two domains with 
> 1GB of RAM each, then your backend would need at least 2GB + some for 
> its own purpose.
> This probably wants to be resolved by allowing foreign mapping to be 
> "paging" out as you would for memory assigned to a userspace. 
Didn't notice the last sentence initially. Could you please explain your 
idea in detail if possible. Does it mean if implemented it would be 
feasible to map all guest memory regardless of how much memory the guest 
has? Avoiding map/unmap memory each guest request would allow us to have 
better performance (of course with taking care of the fact that guest 
memory layout could be changed)... Actually what I understand looking at 
kvmtool is the fact it does not map/unmap memory dynamically, just 
calculate virt addresses according to the gfn provided.

--
Regards,

Oleksandr Tyshchenko