Re: [Xen-devel] [PATCH v2 03/16] Xen: xlate: Use page_to_xen_pfn instead of page_to_pfn

[Shannon Zhao]

On 2016/1/19 22:59, Stefano Stabellini wrote:
> On Mon, 18 Jan 2016, Shannon Zhao wrote:
> > On 2016/1/16 1:08, Stefano Stabellini wrote:
> > > On Fri, 15 Jan 2016, Shannon Zhao wrote:
> > > > From: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> > > >
> > > > Use page_to_xen_pfn in case of 64KB page.
> > > >
> > > > Signed-off-by: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> > > > ---
> > > >   drivers/xen/xlate_mmu.c | 2 +-
> > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> > > > index 9692656..b9fcc2c 100644
> > > > --- a/drivers/xen/xlate_mmu.c
> > > > +++ b/drivers/xen/xlate_mmu.c
> > > > @@ -227,7 +227,7 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, void **virt,
> > > >   		return rc;
> > > >   	}
> > > >   	for (i = 0; i < nr_grant_frames; i++)
> > > > -		pfns[i] = page_to_pfn(pages[i]);
> > > > +		pfns[i] = page_to_xen_pfn(pages[i]);
> > >
> > > Shannon, thanks for the patch.
> > >
> > > Keeping in mind that in the 64K case, kernel pages are 64K but xen pages
> > > are still 4K, I think you also need to allocate
> > > (nr_grant_frames/XEN_PFN_PER_PAGE) kernel pages (assuming that they are
> > > allocated contiguously): nr_grant_frames refers to 4K pages, while
> > > xen_xlate_map_ballooned_pages is allocating pages on a 64K granularity
> > > (sizeof(pages[0]) == 64K).
> > >
> > > Be careful that alloc_xenballooned_pages deals with 64K pages (because
> > > it deals with kernel pages), while xen_pfn_t is always 4K based (because
> > > it deals with Xen pfns).
> > >
> > > Please test it with and without CONFIG_ARM64_64K_PAGES. Thanks!
> > Stefano, thanks for your explanation. How about below patch?
>
> Good work, it looks like you covered all bases, I think it should work,
> but I haven't tested it myself. Just one note below.
>
>
> > diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> > index 9692656..e1f7c95 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] = xen_pfn++;
> > +       }
>
> We might want to:
>
>    pfns[i] = pfn_to_gfn(xen_pfn++);
>
> for consistency, even though for autotranslate guests pfn_to_gfn always
> returns pfn.
Ok, will add. Thanks.

> > -       vaddr = vmap(pages, nr_grant_frames, 0, PAGE_KERNEL);
> > +       vaddr = vmap(pages, nr_pages, 0, PAGE_KERNEL);
> >          if (!vaddr) {
> > -               pr_warn("%s Couldn't map %ld pfns rc:%d\n", __func__,
> > -                       nr_grant_frames, rc);
> > -               free_xenballooned_pages(nr_grant_frames, pages);
> > +               pr_warn("%s Couldn't map %ld pages rc:%d\n", __func__,
> > +                       nr_pages, rc);
> > +               free_xenballooned_pages(nr_pages, pages);
> >                  kfree(pages);
> >                  kfree(pfns);
> >                  return -ENOMEM;
> >
> > --
> > Shannon

--
Shannon