Re: [Xen-devel] [PATCH] xen/arm: Allow balooning working with 1:1 memory mapping

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/14/2013 03:34 PM, Stefano Stabellini wrote:
> On Thu, 14 Nov 2013, Julien Grall wrote:
> > With the lake of iommu, dom0 must have a 1:1 memory mapping for all
> > these guest physical address. When the ballon decides to give back a
> > page to the kernel, this page must have the same address as previously.
> > Otherwise, we will loose the 1:1 mapping and will break DMA-capable
> > device.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> > CC: Keir Fraser <keir@xxxxxxx>
> > CC: Jan Beulich <jbeulich@xxxxxxxx>
> > ---
> >   xen/common/memory.c | 42 ++++++++++++++++++++++++++++++++++++++++--
> >   1 file changed, 40 insertions(+), 2 deletions(-)
> >
> > diff --git a/xen/common/memory.c b/xen/common/memory.c
> > index 50b740f..df36d43 100644
> > --- a/xen/common/memory.c
> > +++ b/xen/common/memory.c
> > @@ -28,6 +28,9 @@
> >   #include <public/memory.h>
> >   #include <xsm/xsm.h>
> >   #include <xen/trace.h>
> > +#ifdef CONFIG_ARM
> > +#include <asm/platform.h>
> > +#endif
> >
> >   struct memop_args {
> >       /* INPUT */
> > @@ -90,7 +93,7 @@ static void increase_reservation(struct memop_args *a)
> >
> >   static void populate_physmap(struct memop_args *a)
> >   {
> > -    struct page_info *page;
> > +    struct page_info *page = NULL;
> >       unsigned long i, j;
> >       xen_pfn_t gpfn, mfn;
> >       struct domain *d = a->domain;
> > @@ -122,7 +125,33 @@ static void populate_physmap(struct memop_args *a)
> >           }
> >           else
> >           {
> > -            page = alloc_domheap_pages(d, a->extent_order, a->memflags);
> > +#ifdef CONFIG_ARM
> > +            if ( d == dom0 && 
> > platform_has_quirk(PLATFORM_QUIRK_DOM0_MAPPING_11) )
> > +            {
> > +                mfn = gpfn;
> > +                if (!mfn_valid(mfn))
> > +                {
> > +                    gdprintk(XENLOG_INFO, "Invalid mfn 0x%"PRI_xen_pfn"\n",
> > +                             mfn);
> > +                    goto out;
> > +                }
> > +
> > +                page = mfn_to_page(mfn);
> > +                if ( !get_page(page, d) )
> > +                {
> > +                    gdprintk(XENLOG_INFO,
> > +                             "mfn 0x%"PRI_xen_pfn" doesn't belong to dom0\n",
> > +                             mfn);
> > +                    goto out;
> > +                }
> > +                put_page(page);
> > +            }
> > +            else
> > +#endif
> I don't know if the x86 maintainers would like that, but I would prefer
> to remove the ifdef CONFIG_ARM.
> You just need to define a new function called is_dom0_mapped_11, that
> always returns false on x86 and on ARM is implemented by d == dom0 &&
> platform_has_quirk(PLATFORM_QUIRK_DOM0_MAPPING_11).
> Then you can use it on common code.
With this solution, it's less clear that it's ARM specific code. We are 
introducing a workaround that will never be used on x86.
I would wait an opinion from other maintainers before sending a new 
version of this patch.
--
Julien Grall

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