[Xen-devel] [PATCH v2 1/2] x86/altp2m: use __get_gfn_type_access to avoid lock conflicts

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

From: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

Use __get_gfn_type_access instead of get_gfn_type_access when checking
the hostp2m entries during altp2m mem_access setting and gfn remapping
to avoid a lock conflict which can make dom0 freeze. During mem_access
setting the hp2m is already locked. For gfn remapping we change the flow
to lock the hp2m before locking the ap2m.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
Reviewed-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

v2: Lock the hp2m during gfn remapping
---
 xen/arch/x86/mm/p2m.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 812dbf6..1eeb934 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1787,8 +1787,8 @@ int p2m_set_altp2m_mem_access(struct domain *d, struct 
p2m_domain *hp2m,
     if ( !mfn_valid(mfn) )
     {
 
-        mfn = get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
-                                  P2M_ALLOC | P2M_UNSHARE, &page_order);
+        mfn = __get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
+                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 0);
 
         rc = -ESRCH;
         if ( !mfn_valid(mfn) || t != p2m_ram_rw )
@@ -2548,6 +2548,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned int 
idx,
     hp2m = p2m_get_hostp2m(d);
     ap2m = d->arch.altp2m_p2m[idx];
 
+    p2m_lock(hp2m);
     p2m_lock(ap2m);
 
     mfn = ap2m->get_entry(ap2m, gfn_x(old_gfn), &t, &a, 0, NULL, NULL);
@@ -2563,8 +2564,8 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned int 
idx,
     /* Check host p2m if no valid entry in alternate */
     if ( !mfn_valid(mfn) )
     {
-        mfn = get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
-                                  P2M_ALLOC | P2M_UNSHARE, &page_order);
+        mfn = __get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
+                                    P2M_ALLOC | P2M_UNSHARE, &page_order, 0);
 
         if ( !mfn_valid(mfn) || t != p2m_ram_rw )
             goto out;
@@ -2606,6 +2607,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned int 
idx,
 
  out:
     p2m_unlock(ap2m);
+    p2m_unlock(hp2m);
     return rc;
 }
 
-- 
2.8.1


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