[Xen-devel] [RFC PATCH 3/4] x86/p2m : remove checks that forbid adding foreign pages between HVM guests

[Zhongze Liu <blackskygg@xxxxxxxxx>]

Two checks in the p2m code forbids sharing physical pages among DomU's by using
xc_add_to_physmap_batch with XENMAPSPACE_gmfn_foreign. Just simply remove them
in this RFC patch to ask for suggestions on how to properly handle this.

This is for the proposal "Allow setting up shared memory areas between VMs
from xl config file" (see [1]).

[1] https://lists.xenproject.org/archives/html/xen-devel/2017-07/msg03047.html

Signed-off-by: Zhongze Liu <blackskygg@xxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxx
---
 xen/arch/x86/mm/p2m.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index e8a57d118c..3ee4c14ed4 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -2531,8 +2531,13 @@ int p2m_add_foreign(struct domain *tdom, unsigned long 
fgfn,
      * hvm fixme: until support is added to p2m teardown code to cleanup any
      * foreign entries, limit this to hardware domain only.
      */
-    if ( !is_hardware_domain(tdom) )
-        return -EPERM;
+    /* The following check prevents us from doing a XENMEM_add_to_physmap
+     * between two domU's. Asking for suggestions on how to remove or
+     * work around it.
+     *
+     *     if ( !is_hardware_domain(tdom) )
+     *         return -EPERM;
+     */
 
     if ( foreigndom == DOMID_XEN )
         fdom = rcu_lock_domain(dom_xen);
@@ -2545,9 +2550,14 @@ int p2m_add_foreign(struct domain *tdom, unsigned long 
fgfn,
     if ( tdom == fdom )
         goto out;
 
-    rc = xsm_map_gmfn_foreign(XSM_TARGET, tdom, fdom);
-    if ( rc )
-        goto out;
+    /* The following check prevents us from doing a XENMEM_add_to_physmap
+     * between two domU's. Asking for suggestions on how to remove or
+     * work around it.
+     *
+     *  rc = xsm_map_gmfn_foreign(XSM_TARGET, tdom, fdom);
+     *  if ( rc )
+     *      goto out;
+     */
 
     /*
      * Take a refcnt on the mfn. NB: following supported for foreign mapping:
-- 
2.13.3


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel