x86/ldt: Make modify_ldt synchronous

[pandora-kernel.git] / arch / x86 / include / asm / mmu_context.h

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 6902152..ce4ea94 100644 (file)
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -15,6 +15,51 @@ static inline void paravirt_activate_mm(struct mm_struct *prev,
 }
 #endif /* !CONFIG_PARAVIRT */
 
+/*
+ * ldt_structs can be allocated, used, and freed, but they are never
+ * modified while live.
+ */
+struct ldt_struct {
+       /*
+        * Xen requires page-aligned LDTs with special permissions.  This is
+        * needed to prevent us from installing evil descriptors such as
+        * call gates.  On native, we could merge the ldt_struct and LDT
+        * allocations, but it's not worth trying to optimize.
+        */
+       struct desc_struct *entries;
+       int size;
+};
+
+static inline void load_mm_ldt(struct mm_struct *mm)
+{
+       struct ldt_struct *ldt;
+
+       /* smp_read_barrier_depends synchronizes with barrier in install_ldt */
+       ldt = ACCESS_ONCE(mm->context.ldt);
+       smp_read_barrier_depends();
+
+       /*
+        * Any change to mm->context.ldt is followed by an IPI to all
+        * CPUs with the mm active.  The LDT will not be freed until
+        * after the IPI is handled by all such CPUs.  This means that,
+        * if the ldt_struct changes before we return, the values we see
+        * will be safe, and the new values will be loaded before we run
+        * any user code.
+        *
+        * NB: don't try to convert this to use RCU without extreme care.
+        * We would still need IRQs off, because we don't want to change
+        * the local LDT after an IPI loaded a newer value than the one
+        * that we can see.
+        */
+
+       if (unlikely(ldt))
+               set_ldt(ldt->entries, ldt->size);
+       else
+               clear_LDT();
+
+       DEBUG_LOCKS_WARN_ON(preemptible());
+}
+
 /*
  * Used for LDT copy/destruction.
  */
@@ -52,7 +97,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
                 * load the LDT, if the LDT is different:
                 */
                if (unlikely(prev->context.ldt != next->context.ldt))
-                       load_LDT_nolock(&next->context);
+                       load_mm_ldt(next);
        }
 #ifdef CONFIG_SMP
        else {
@@ -65,7 +110,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
                         * to make sure to use no freed page tables.
                         */
                        load_cr3(next->pgd);
-                       load_LDT_nolock(&next->context);
+                       load_mm_ldt(next);
                }
        }
 #endif