ldt optimization

@@ -466,23 +466,6 @@
 }
 
 /*
- * No need to lock the MM as we are the last user
- */
-void release_segments(struct mm_struct *mm)
-{
-	void * ldt = mm->context.segments;
-
-	/*
-	 * free the LDT
-	 */
-	if (ldt) {
-		mm->context.segments = NULL;
-		clear_LDT();
-		vfree(ldt);
-	}
-}
-
-/*
  * Create a kernel thread
  */
 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)

@@ -534,45 +517,19 @@
 void release_thread(struct task_struct *dead_task)
 {
 	if (dead_task->mm) {
-		void * ldt = dead_task->mm->context.segments;
-
 		// temporary debugging check
-		if (ldt) {
-			printk("WARNING: dead process %8s still has LDT? <%p>\n",
-					dead_task->comm, ldt);
+		if (dead_task->mm->context.size) {
+			printk("WARNING: dead process %8s still has LDT? <%p/%d>\n",
+					dead_task->comm,
+					dead_task->mm->context.ldt,
+					dead_task->mm->context.size);
 			BUG();
 		}
 	}
-
 	release_x86_irqs(dead_task);
 }
 
 /*
- * we do not have to muck with descriptors here, that is
- * done in switch_mm() as needed.
- */
-void copy_segments(struct task_struct *p, struct mm_struct *new_mm)
-{
-	struct mm_struct * old_mm;
-	void *old_ldt, *ldt;
-
-	ldt = NULL;
-	old_mm = current->mm;
-	if (old_mm && (old_ldt = old_mm->context.segments) != NULL) {
-		/*
-		 * Completely new LDT, we initialize it from the parent:
-		 */
-		ldt = vmalloc(LDT_ENTRIES*LDT_ENTRY_SIZE);
-		if (!ldt)
-			printk(KERN_WARNING "ldt allocation failed\n");
-		else
-			memcpy(ldt, old_ldt, LDT_ENTRIES*LDT_ENTRY_SIZE);
-	}
-	new_mm->context.segments = ldt;
-	new_mm->context.cpuvalid = ~0UL;	/* valid on all CPU's - they can't have stale data */
-}
-
-/*
  * Save a segment.
  */
 #define savesegment(seg,value) \

196 lines not on this page · raw message

@@ -4,10 +4,13 @@
 /*
  * The i386 doesn't have a mmu context, but
  * we put the segment information here.
+ *
+ * cpu_vm_mask is used to optimize ldt flushing.
  */
 typedef struct { 
-	void *segments;
-	unsigned long cpuvalid;
+	int size;
+	struct semaphore sem;
+	void *	ldt;
 } mm_context_t;
 
 #endif

@@ -79,13 +79,13 @@
 /*
  * load one particular LDT into the current CPU
  */
-static inline void load_LDT (struct mm_struct *mm)
+static inline void load_LDT (mm_context_t *pc)
 {
 	int cpu = smp_processor_id();
-	void *segments = mm->context.segments;
-	int count = LDT_ENTRIES;
+	void *segments = pc->ldt;
+	int count = pc->size;
 
-	if (!segments) {
+	if (!count) {
 		segments = &default_ldt[0];
 		count = 5;
 	}

@@ -7,10 +7,12 @@
 #include <asm/pgalloc.h>
 
 /*
- * possibly do the LDT unload here?
+ * hooks to add arch specific data into the mm struct.
+ * Note that destroy_context is called even if init_new_context
+ * fails.
  */
-#define destroy_context(mm)		do { } while(0)
-#define init_new_context(tsk,mm)	0
+int init_new_context(struct task_struct *tsk, struct mm_struct *mm);
+void destroy_context(struct mm_struct *mm);
 
 #ifdef CONFIG_SMP
 

@@ -30,19 +32,18 @@
 	if (prev != next) {
 		/* stop flush ipis for the previous mm */
 		clear_bit(cpu, &prev->cpu_vm_mask);
-		/*
-		 * Re-load LDT if necessary
-		 */
-		if (prev->context.segments != next->context.segments)
-			load_LDT(next);
 #ifdef CONFIG_SMP
 		cpu_tlbstate[cpu].state = TLBSTATE_OK;
 		cpu_tlbstate[cpu].active_mm = next;
 #endif
 		set_bit(cpu, &next->cpu_vm_mask);
-		set_bit(cpu, &next->context.cpuvalid);
 		/* Re-load page tables */
 		load_cr3(next->pgd);
+	 	/* load_LDT, if either the previous or next thread
+		 * has a non-default LDT.
+		 */
+		if (next->context.size+prev->context.size)
+			load_LDT(&next->context);
 	}
 #ifdef CONFIG_SMP
 	else {

@@ -54,9 +55,8 @@
 			 * tlb flush IPI delivery. We must reload %cr3.
 			 */
 			load_cr3(next->pgd);
+			load_LDT(&next->context);
 		}
-		if (!test_and_set_bit(cpu, &next->context.cpuvalid))
-			load_LDT(next);
 	}
 #endif
 }

@@ -435,9 +435,12 @@
  */
 extern int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags);
 
-/* Copy and release all segment info associated with a VM */
-extern void copy_segments(struct task_struct *p, struct mm_struct * mm);
-extern void release_segments(struct mm_struct * mm);
+/* Copy and release all segment info associated with a VM
+ * Unusable due to lack of error handling, use {init_new,destroy}_context
+ * instead.
+ */
+static inline void copy_segments(struct task_struct *p, struct mm_struct * mm) { }
+static inline void release_segments(struct mm_struct * mm) { }
 
 /*
  * Return saved PC of a blocked thread.

@@ -20,7 +20,7 @@
    of the stack frame of math_emulate() */
 #define SETUP_DATA_AREA(arg)	FPU_info = (struct info *) &arg
 
-#define LDT_DESCRIPTOR(s)	(((struct desc_struct *)current->mm->context.segments)[(s) >> 3])
+#define LDT_DESCRIPTOR(s)	(((struct desc_struct *)current->mm->context.ldt)[(s) >> 3])
 #define SEG_D_SIZE(x)		((x).b & (3 << 21))
 #define SEG_G_BIT(x)		((x).b & (1 << 23))
 #define SEG_GRANULARITY(x)	(((x).b & (1 << 23)) ? 4096 : 1)