Re: [Xen-devel] RT Xen on ARM - R-Car series

[Julien Grall <julien.grall@xxxxxxx>]

On 2/1/19 10:35 AM, Andrii Anisov wrote:
> Hello,
Hi,

> On 01.02.19 12:12, Julien Grall wrote:
> > This is actually a shared page, the page is allocated by the domain 
> > and shared with Xen. So what do you mean?
> I'm curious if it can be allocated on hypervisor side.
There are very limited case where the hypervisor is allocating memory to 
share with the guest. In general, we want to account the memory to the 
guest, so the best way is to let the guest provide the buffer.
In that case this will not help because the hypercall is taking a 
virtual address (not a guest virtual frame, nor guest physical frame!). 
So the buffer can span across the page-boundary or even have the mapping 
changed.
We can possibly add a restriction on the mapping not changing (pending 
investigation). But I think requesting the address to be page-aligned is 
going to be hard because the runstate is not filling a page.
For instance, Linux is using a per-cpu variable for that. I am not 
entirely sure whether it promise the structure will never cross a 
page-boundary.
> > That's not a link but a Message-ID. You can either use your favorite 
> > client for looking the e-mail
> It only works if you have it in the current mailbox, I guess.

That's correct.

Cheers,

--
Julien Grall

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