Re: [PATCH v7 03/17] Xen: xlate: Use page_to_xen_pfn instead of page_to_pfn

[Julien Grall]

Hi Shannon,

On 30/03/16 08:38, Shannon Zhao wrote:
> On 2016/3/30 0:28, Julien Grall wrote:
> > On 24/03/16 14:44, Shannon Zhao wrote:
> > > Make xen_xlate_map_ballooned_pages work with 64K pages. In that case
> > > Kernel pages are 64K in size but Xen pages remain 4K in size. Xen pfns
> > > refer to 4K pages.
> > >
> > > Signed-off-by: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> > > Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > > ---
> > >    drivers/xen/xlate_mmu.c | 26 ++++++++++++++++----------
> > >    1 file changed, 16 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> > > index 9692656..28f728b 100644
> > > --- a/drivers/xen/xlate_mmu.c
> > > +++ b/drivers/xen/xlate_mmu.c
> > > @@ -207,9 +207,12 @@ int __init
> > > xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, void **virt,
> > >        void *vaddr;
> > >        int rc;
> > >        unsigned int i;
> > > +    unsigned long nr_pages;
> > > +    xen_pfn_t xen_pfn = 0;
> > >
> > >        BUG_ON(nr_grant_frames == 0);
> > > -    pages = kcalloc(nr_grant_frames, sizeof(pages[0]), GFP_KERNEL);
> > > +    nr_pages = DIV_ROUND_UP(nr_grant_frames, XEN_PFN_PER_PAGE);
> > > +    pages = kcalloc(nr_pages, sizeof(pages[0]), GFP_KERNEL);
> > >        if (!pages)
> > >            return -ENOMEM;
> > >
> > > @@ -218,22 +221,25 @@ int __init
> > > xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, void **virt,
> > >            kfree(pages);
> > >            return -ENOMEM;
> > >        }
> > > -    rc = alloc_xenballooned_pages(nr_grant_frames, pages);
> > > +    rc = alloc_xenballooned_pages(nr_pages, pages);
> > >        if (rc) {
> > > -        pr_warn("%s Couldn't balloon alloc %ld pfns rc:%d\n", __func__,
> > > -            nr_grant_frames, rc);
> > > +        pr_warn("%s Couldn't balloon alloc %ld pages rc:%d\n", __func__,
> > > +            nr_pages, rc);
> > >            kfree(pages);
> > >            kfree(pfns);
> > >            return rc;
> > >        }
> > > -    for (i = 0; i < nr_grant_frames; i++)
> > > -        pfns[i] = page_to_pfn(pages[i]);
> > > +    for (i = 0; i < nr_grant_frames; i++) {
> > > +        if ((i % XEN_PFN_PER_PAGE) == 0)
> > > +            xen_pfn = page_to_xen_pfn(pages[i / XEN_PFN_PER_PAGE]);
> > > +        pfns[i] = pfn_to_gfn(xen_pfn++);
> > > +    }
> >
> > Would it be possible to re-use xen_for_each_gfn? This will avoid
> > open-coding the loop to break down the Linux page.
> I don't think so. Using xen_acpi_guest_init will require factoring
> "pfns[i] = pfn_to_gfn(xen_pfn++)" to a function with parameter pfns[i].
> How can we pass pfns[i]?

By using the variable data. Something along those lines:

struct map_balloon_pages
{
      xen_pfn_t *pfns;
      unsigned int idx;
};

static void setup_balloon_gfn(unsigned long gfn, void *data)
{
      struct map_balloon_pages *info = data;


      data->pfns[data->idx] = gfn;
      data->idx++;
}

And then in xen_xlate_map_ballooned_pages

xen_for_each_gfn(pages, nr_grant_frames, setup_balloon_gfn, &data);

Regards,

--
Julien Grall