[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH 7/8] xen/arm: Set foreign page type to p2m_map_foreign

On 12/05/2013 04:34 PM, Ian Campbell wrote:
On Thu, 2013-12-05 at 15:42 +0000, Julien Grall wrote:
Xen needs to know that the current page belongs to another domain. Also take
the refcount to this page.

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
  xen/arch/arm/mm.c |   14 +++++++++-----
  1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 960c872..bf383a7 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -977,6 +977,7 @@ static int xenmem_add_to_physmap_one(
      unsigned long mfn = 0;
      int rc;
+    p2m_type_t t = p2m_ram_rw;

Can we set this explicitly on a per-mapspace basis please, so the
compiler will complain about an uninitialised variable if we forget to
add the type for a new map space, instead of silently creating writable
ram mappings.

Will do.

      switch ( space )
@@ -1019,8 +1020,8 @@ static int xenmem_add_to_physmap_one(
      case XENMAPSPACE_gmfn_foreign:
-        paddr_t maddr;
          struct domain *od;
+        struct page_info *page;
          od = rcu_lock_domain_by_any_id(foreign_domid);
          if ( od == NULL )
              return -ESRCH;
@@ -1032,15 +1033,18 @@ static int xenmem_add_to_physmap_one(
              return rc;

-        maddr = p2m_lookup(od, pfn_to_paddr(idx));
-        if ( maddr == INVALID_PADDR )
+        /* Take refcount to the foreign domain page.

"on the foreign" (and maybe "domain's" or just "foreign page"

+         * Refcount will be release in XENMEM_remove_from_physmap */

"will be released".

The refcount will also be removed by p2m_teardown. That probably needs
changing to do an actual walk of the p2m tearing things down, which is a

Stefano's now obsolete dma pinning series had a patch which added a
fairly generic walker in it which might be reusable.

Do you have a link to this patch?

The walk might need to support continuations though.

I wonder if this ref ought to be taken in create_p2m_entries for all
entries and not just foreign ones, and then released in the appropriate

If I'm not mistaken, Xen already takes a ref when the page is allocated for the domain. Why would we need to take another ref for these pages?

Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.