Re: [Xen-devel] [PATCH] xen/arm: remove special dom0 case in dump_hyp_walk

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 10/15/19 4:51 PM, Stefano Stabellini wrote:
> On Tue, 15 Oct 2019, Julien Grall wrote:
> > Hi Stefano,
> >
> > On 10/15/19 4:49 AM, Stefano Stabellini wrote:
> > > There is no need to have a special dom0 case to convert the pgtable
> > > virtual address into a physical address. The virt_to_maddr function can
> > > work both in the dom0 case and the domU case.
> > >
> > > This is more than a cleanup: when Xen is loaded at addresses lower than
> > > 2MB on arm32 phys_offset might not hold the right value and be unable to
> > > perform a virt to phys conversion properly. Reducing the unnecessary
> > > usage of phys_offset is a good idea.
> > Aside what Juergen said, this paragraph raises the question why phys_offset is
> > actually not modified (or completely dropped)? After all, if the value holds
> > is wrong then other users may get wrong value as well...
> Should I add something like "this is not a fix, but reducing unnecessary[...]" ?
dump_hyp_walk() is only used in two places:
    - when hardware translation failed
    - Hypervisor data abort

In both case we will panic afterwards. So hitting the BUG_ON() is just 
only a matter of losing page-table information.
So I see limited reason to see this patch alone in Xen 4.13. We should 
either completely fix phys_offset or do nothing.
Cheers,

--
Julien Grall

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