Re: [Xen-devel] [PATCH v4 6/7] xen/arm: don't iomem_permit_access for reserved-memory regions

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 12 Aug 2019, Julien Grall wrote:
> On 09/08/2019 23:56, Stefano Stabellini wrote:
> > On Thu, 8 Aug 2019, Volodymyr Babchuk wrote:
> > > Hi Stefano,
> > > 
> > > Stefano Stabellini writes:
> > > 
> > > > Don't allow reserved-memory regions to be remapped into any guests,
> > > > until reserved-memory regions are properly supported in Xen. For now,
> > > > do not call iomem_permit_access for them.
> > > > 
> > > > Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> > > > ---
> > > > 
> > > > Changes in v4:
> > > > - compare the parent name with reserved-memory
> > > > - use dt_node_cmp
> > > > 
> > > > Changes in v3:
> > > > - new patch
> > > > ---
> > > >   xen/arch/arm/domain_build.c | 24 ++++++++++++++++--------
> > > >   1 file changed, 16 insertions(+), 8 deletions(-)
> > > > 
> > > > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > > > index 4c8404155a..267e0549e2 100644
> > > > --- a/xen/arch/arm/domain_build.c
> > > > +++ b/xen/arch/arm/domain_build.c
> > > > @@ -1153,17 +1153,25 @@ static int __init map_range_to_domain(const
> > > > struct dt_device_node *dev,
> > > >       struct map_range_data *mr_data = data;
> > > >       struct domain *d = mr_data->d;
> > > >       bool need_mapping = !dt_device_for_passthrough(dev);
> > > > +    const struct dt_device_node *parent = dt_get_parent(dev);
> > > >       int res;
> > > > 
> > > > -    res = iomem_permit_access(d, paddr_to_pfn(addr),
> > > > -                              paddr_to_pfn(PAGE_ALIGN(addr + len -
> > > > 1)));
> > > > -    if ( res )
> > > > +    /*
> > > > +     * Don't give iomem permissions for reserved-memory ranges until
> > > > +     * reserved-memory support is complete.
> > > > +     */
> > > > +    if ( dt_node_cmp(dt_node_name(parent), "reserved-memory") == 0 )
> > > Am I missing something, or you are permitting access only if it from a
> > > "reserved-memory" node? This contradicts with patch description.
> > 
> > Well spotted! I inverted the condition by mistake.
> > 
> > 
> > > >       {
> > > > -        printk(XENLOG_ERR "Unable to permit to dom%d access to"
> > > > -               " 0x%"PRIx64" - 0x%"PRIx64"\n",
> > > > -               d->domain_id,
> > > > -               addr & PAGE_MASK, PAGE_ALIGN(addr + len) - 1);
> > > > -        return res;
> > > > +        res = iomem_permit_access(d, paddr_to_pfn(addr),
> > > > +                                  paddr_to_pfn(PAGE_ALIGN(addr + len -
> > > > 1)));
> > > > +        if ( res )
> > > > +        {
> > > > +            printk(XENLOG_ERR "Unable to permit to dom%d access to"
> > > > +                   " 0x%"PRIx64" - 0x%"PRIx64"\n",
> > > > +                   d->domain_id,
> > > > +                   addr & PAGE_MASK, PAGE_ALIGN(addr + len) - 1);
> > > > +            return res;
> > > > +        }
> > > >       }
> > > > 
> > > >       if ( need_mapping )
> > > So, this region cold be mapped, but without the access?
> 
> IOMEM access and mapping are two different things. The former gives a domain
> control over managing the region (i.e mapping, unmapping, giving access to
> another domain). The latter will map the region in the P2M so the domain can
> read/write into it.
> 
> > 
> > I'll change it to return early from the function for reserved-memory
> > regions.
> 
> I am not sure to understand you suggestion here... You still need to have
> reserved-regions mapped into the hardware domain. The only thing we want to
> prevent is the domain to manage the region.

I forgot that giving iomem permission to dom0 automatically means that
the toolstack can give iomem permission to a domU for the same region.

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