Re: [Xen-devel] [PATCH RFC v2] Add SUPPORT.md

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 12/09/2017 20:52, Stefano Stabellini wrote:
> On Tue, 12 Sep 2017, Roger Pau Monné wrote:
> > On Mon, Sep 11, 2017 at 06:01:59PM +0100, George Dunlap wrote:
> > > +## Scalability
> > > +
> > > +### 1GB/2MB super page support
> > > +
> > > +    Status: Supported
> > This needs something like:
> >
> > Status, x86 HVM/PVH: Supported
> >
> > IIRC on ARM page sizes are different (64K?)
> There is a separate entry for different page granularities. 2MB and 1GB
> super-pages, both based on 4K granularity, are supported on ARM too.
This entry and the entry "ARM: 16K and 64K pages in guests" are two 
different things.
Here we speak about the hypervisor whereas the other one is about guests 
itself.
At the moment, the hypervisor only supports 4K. The guests can support 
4K, 16K, 64K. The later two are only for AArch64 guest.
It is probably worth to rename the other entry to "ARM: 4K, 16K, 64K 
pages in guests" for avoiding confusion.
[...]

> > > +### ARM: 16K and 64K pages in guests
> > > +
> > > +    Status: Supported, with caveats
> > > +
> > > +No support for QEMU backends in a 16K or 64K domain.
> > Needs to be merged with the "1GB/2MB super page support"?
> Super-pages are different from page granularity. 1GB and 2MB pages are
> based on the same 4K page granularity, while 512MB pages are based on
> 64K granularity. Does it make sense?
> Maybe we want to say "ARM: 16K and 64K page granularity in guest" to
> clarify.
Each entry is related to different components. The first entry is about 
the hypervisor, whilst this one is about guests. We really don't care 
whether the guests is going to use superpage because at the end of the 
day this will get handle by the hardware directly.
The only thing we care is those guests to be able to interact with Xen 
(the interface is based on 4K granularity at the moment).
So I am not sure what we are trying to clarify at the end...

Cheers,

--
Julien Grall

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