Re: [Xen-devel] [PATCH 06/12] xen: mark grant mapped pages as foreign

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 9 Jan 2015, David Vrabel wrote:
> On 09/01/15 16:19, Ian Campbell wrote:
> > On Fri, 2015-01-09 at 16:03 +0000, Stefano Stabellini wrote:
> >> On Tue, 6 Jan 2015, David Vrabel wrote:
> >>> From: Jenny Herbert <jennifer.herbert@xxxxxxxxxx>
> >>>
> >>> Use the "foreign" page flag to mark pages that have a grant map.  Use
> >>> page->private to store information of the grant (the granting domain
> >>> and the grant reference).
> >>>
> >>> Signed-off-by: Jenny Herbert <jenny.herbert@xxxxxxxxxx>
> >>> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> >>> ---
> >>>  arch/x86/xen/p2m.c        |   50 
> >>> ++++++++++++++++++++++++++++++++++++++-------
> >>>  include/xen/grant_table.h |   13 ++++++++++++
> >>>  2 files changed, 56 insertions(+), 7 deletions(-)
> >>>
> >>> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> >>> index 0d70814..22624a3 100644
> >>> --- a/arch/x86/xen/p2m.c
> >>> +++ b/arch/x86/xen/p2m.c
> >>> @@ -648,6 +648,43 @@ bool set_phys_to_machine(unsigned long pfn, unsigned 
> >>> long mfn)
> >>>   return true;
> >>>  }
> >>>  
> >>> +static int
> >>> +init_page_grant_ref(struct page *p, domid_t domid, grant_ref_t grantref)
> >>> +{
> >>> +#ifdef CONFIG_X86_64
> >>> + uint64_t gref;
> >>> + uint64_t* gref_p = &gref;
> >>> +#else
> >>> + uint64_t* gref_p = kmalloc(sizeof(uint64_t), GFP_KERNEL);
> >>> + if (!gref)
> >>> +         return -ENOMEM;
> >>> + uint64_t* gref = gref_p;
> >>> +#endif
> >>> +
> >>> + *gref_p = ((uint64_t) grantref << 32) | domid;
> >>> + p->private = gref;
> >>> +
> >>> + WARN_ON(PagePrivate(p));
> >>> + WARN_ON(PageForeign(p));
> >>> + SetPagePrivate(p);
> >>> + SetPageForeign(p);
> >>> + return 0;
> >>> +}
> >>> +
> >>> +static void
> >>> +clear_page_grant_ref(struct page *p)
> >>> +{
> >>> + WARN_ON(!PagePrivate(p));
> >>> + WARN_ON(!PageForeign(p));
> >>> +
> >>> +#ifndef CONFIG_X86_64
> >>> + kfree(p->private);
> >>> +#endif
> >>> + p->private = 0;
> >>> + ClearPagePrivate(p);
> >>> + ClearPageForeign(p);
> >>> +}
> >>
> >> Given that get_page_grant_ref is used by netback, these functions need
> >> to be made arch-independent, moved to an arch-independent code location
> >> and called appropriately.
> 
> I've fixed this already.
> 
> > ... or stubbed out for arches which don't need this (which might include
> > arm*?).
> 
> I'm reasonably certain that this is required for HVM and ARM guests as
> well.  The grant copy will still fail to get the page by gfn since the
> mfn is owned by a different domain.

I agree

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