Re: [Xen-devel] [PATCH 05/10] xen/arm: vgic-v3: Document the current restrictions

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2015-01-21 at 12:33 +0000, Julien Grall wrote:
> On 21/01/15 12:16, Ian Campbell wrote:
> > On Tue, 2015-01-20 at 17:49 +0000, Julien Grall wrote:
> > 
> >>>>     - A processor can only access his own redistributor. For buggy
> >>>>     assumption, the current code bank the redistributors MMIO.
> >>>
> >>> What assumption? It's not clear if you mean that a foreign redistributor
> >>> should not be accessible and is, or if it should be accessible and
> >>> isn't.
> >>
> >> Every redistributor (one per processor) are mapped in distinct MMIO region.
> >>
> >> Unlike the distributor, the redistributor is not banked.
> > 
> > Understood.
> > 
> >> Our current implementation (see vgic_v3_rdistr_mmio_write) consider that
> >> the redistributor is banked and replicate n-times in the memory.
> > 
> > IOW instead of having e.g. 8 individual redistributors each vcpu sees
> > it's own redistributor 8 times. That does seem a bit dubious.
> 
> It's the current behavior. You can see the difference in linux log. The
> address of each redistributor is the same.

Are you sure that isn't the "redistributor region"? One of those can
contain multiple redistributors, i.e. gic_v3_init sets up a single
region and that propagates to the DTB given to the guest.

So the error is just in the mmio decode stage I think, not in the setup
we are trying to achieve.

> >> If you give a look to the redistributor iniatialization (see Xen and
> >> Linux GICv3 code). The code will go through all the redistributors and
> >> check GICR_TYPER to see if the processor is associated to this
> >> redistributor.
> >>
> >> I'm not sure how the redistributor should behave if it's accessed by
> >> another processor.
> > 
> > Please can you find a spec reference and include it in the clarified
> > version of this item.
> 
> Rather than the distributor, there is multiple redistributor (one per
> processor).
> 
> I think the section 5.4.1 in the GICv3 should answer to this question:
> 
> "Each re-distributor must be allocated at one page for controlling the
> overall behavior of the re-distributor and for controlling physical
> LPIs. The base address of this page is referred to as RD_base. In
> addition, each re-distributor must be also allocated the following
> additional pages".

That doesn't say anything about one CPU touching another's
redistributor.

Ian.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel