5 files changed, 53 insertions, 8 deletions

diff --git a/arch/i386/kernel/paravirt.c b/arch/i386/kernel/paravirt.c
index 7329ec9fcc99..4dfdac4550dd 100644
--- a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -545,6 +545,7 @@ struct paravirt_ops paravirt_ops = {
         .apic_write_atomic = native_apic_write_atomic,
         .apic_read = native_apic_read,
 #endif
+        .set_lazy_mode = (void *)native_nop,
 
         .flush_tlb_user = native_flush_tlb,
         .flush_tlb_kernel = native_flush_tlb_global,
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 23ae198dbbc3..cfae587bf7d2 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -670,14 +670,6 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
         load_TLS(next, cpu);
 
         /*
-         * Restore %gs if needed (which is common)
-         */
-        if (prev->gs | next->gs)
-                loadsegment(gs, next->gs);
-
-        write_pda(pcurrent, next_p);
-
-        /*
          * Now maybe handle debug registers and/or IO bitmaps
          */
         if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)
@@ -686,6 +678,15 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
 
         disable_tsc(prev_p, next_p);
 
+        /*
+         * Leave lazy mode, flushing any hypercalls made here.
+         * This must be done before restoring TLS segments so
+         * the GDT and LDT are properly updated, and must be
+         * done before math_state_restore, so the TS bit is up
+         * to date.
+         */
+        arch_leave_lazy_cpu_mode();
+
         /* If the task has used fpu the last 5 timeslices, just do a full
          * restore of the math state immediately to avoid the trap; the
          * chances of needing FPU soon are obviously high now
@@ -693,6 +694,14 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
         if (next_p->fpu_counter > 5)
                 math_state_restore();
 
+        /*
+         * Restore %gs if needed (which is common)
+         */
+        if (prev->gs | next->gs)
+                loadsegment(gs, next->gs);
+
+        write_pda(pcurrent, next_p);
+
         return prev_p;
 }
 
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 9d774d07d95b..00c23433b39f 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -183,6 +183,19 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
 #endif
 
 /*
+ * A facility to provide batching of the reload of page tables with the
+ * actual context switch code for paravirtualized guests.  By convention,
+ * only one of the lazy modes (CPU, MMU) should be active at any given
+ * time, entry should never be nested, and entry and exits should always
+ * be paired.  This is for sanity of maintaining and reasoning about the
+ * kernel code.
+ */
+#ifndef __HAVE_ARCH_ENTER_LAZY_CPU_MODE
+#define arch_enter_lazy_cpu_mode()      do {} while (0)
+#define arch_leave_lazy_cpu_mode()      do {} while (0)
+#endif
+
+/*
  * When walking page tables, get the address of the next boundary,
  * or the end address of the range if that comes earlier.  Although no
  * vma end wraps to 0, rounded up __boundary may wrap to 0 throughout.
diff --git a/include/asm-i386/paravirt.h b/include/asm-i386/paravirt.h
index 53da276a2ec2..38e5164bd0e7 100644
--- a/include/asm-i386/paravirt.h
+++ b/include/asm-i386/paravirt.h
@@ -146,6 +146,8 @@ struct paravirt_ops
         void (fastcall *pmd_clear)(pmd_t *pmdp);
 #endif
 
+        void (fastcall *set_lazy_mode)(int mode);
+
         /* These two are jmp to, not actually called. */
         void (fastcall *irq_enable_sysexit)(void);
         void (fastcall *iret)(void);
@@ -386,6 +388,19 @@ static inline void pmd_clear(pmd_t *pmdp)
 }
 #endif
 
+/* Lazy mode for batching updates / context switch */
+#define PARAVIRT_LAZY_NONE 0
+#define PARAVIRT_LAZY_MMU  1
+#define PARAVIRT_LAZY_CPU  2
+
+#define  __HAVE_ARCH_ENTER_LAZY_CPU_MODE
+#define arch_enter_lazy_cpu_mode() paravirt_ops.set_lazy_mode(PARAVIRT_LAZY_CPU)
+#define arch_leave_lazy_cpu_mode() paravirt_ops.set_lazy_mode(PARAVIRT_LAZY_NONE)
+
+#define  __HAVE_ARCH_ENTER_LAZY_MMU_MODE
+#define arch_enter_lazy_mmu_mode() paravirt_ops.set_lazy_mode(PARAVIRT_LAZY_MMU)
+#define arch_leave_lazy_mmu_mode() paravirt_ops.set_lazy_mode(PARAVIRT_LAZY_NONE)
+
 /* These all sit in the .parainstructions section to tell us what to patch. */
 struct paravirt_patch {
         u8 *instr;              /* original instructions */
diff --git a/kernel/sched.c b/kernel/sched.c
index 08f86178aa34..0dc757246d89 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1853,6 +1853,13 @@ context_switch(struct rq *rq, struct task_struct *prev,
         struct mm_struct *mm = next->mm;
         struct mm_struct *oldmm = prev->active_mm;
 
+        /*
+         * For paravirt, this is coupled with an exit in switch_to to
+         * combine the page table reload and the switch backend into
+         * one hypercall.
+         */
+        arch_enter_lazy_cpu_mode();
+
         if (!mm) {
                 next->active_mm = oldmm;
                 atomic_inc(&oldmm->mm_count);