Re: [PATCH] xen: arm: remove hardcoded gnttab location from dom0

[Ian Campbell <Ian.Campbell@citrix.com>]

On Wed, 2013-12-04 at 02:18 +0800, Chen Baozi wrote:
> On Dec 3, 2013, at 23:04, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> 
> > The DT provided to guests (including dom0) includes a Xen node which, among
> > other things, describes an MMIO region which can be safely used for grant
> > table mappings (i.e. it is a hole in the physical address space). For domU we
> > provide a hardcoded values based on our hardcoded guest virtual machine
> > layout. However for dom0 we need to fit in with the underlying platform.
> > Leaving this hardcoded was an oversight which on some platforms could result
> > in the grant table overlaying RAM or MMIO regions which are in use by domain
> > 0.
> > 
> > For the 4.4 release do as we did with the dom0 evtchn PPI and provide a hook
> > for the platform code to supply a suitable hardcoded address for the platform
> > (derived from reading the data sheet). Platforms which do not provide the hook
> > get the existing address as a default.
> > 
> > After 4.4 we should switch to selecting a region of host RAM which is not RAM
> > in the guest address map. This should be more flexible and safer but the patch
> > was looking too complex for 4.4.
> > 
> > Platform        Gnttab Address
> > ========        ==============
> > exynos5.c       0xb0000000, confirmed with Julien.
> > sunxi.c         0x01d00000, confirmed in data sheet.
> > midway.c        0xff800000, confirmed with Andre, boot tested.
> > vexpress.c      0xb0000000, existing hardcoded value was selected for vexpress.
> > omap5.c         0xb0000000, no datasheet, looks safe in DTB.
> According to OMAP5432 data sheet, 0x80000000~0xbfffffff is the DRAM 
> address space. So this is Ok.

If this is DRAM address space then it's not OK -- what if the guest has
RAM mapped there?

Looks like there are reserved regions at 0x4b000000 or 0x58800000, which
ought to be suitable I think.


> Acked-by: Chen Baozi <baozich@gmail.com>
> 
> Cheers,
> 
> Baozi