x86/paravirt: flush pending mmu updates on context switch

Impact: allow preemption during lazy mmu updates

If we're in lazy mmu mode when context switching, leave
lazy mmu mode, but remember the task's state in
TIF_LAZY_MMU_UPDATES.  When we resume the task, check this
flag and re-enter lazy mmu mode if its set.

This sets things up for allowing lazy mmu mode while preemptible,
though that won't actually be active until the next change.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

1 files changed, 10 insertions, 3 deletions

diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 5eea9548216..430a0e30577 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -252,7 +252,7 @@ static inline void enter_lazy(enum paravirt_lazy_mode mode)
         __get_cpu_var(paravirt_lazy_mode) = mode;
 }
 
-void paravirt_leave_lazy(enum paravirt_lazy_mode mode)
+static void leave_lazy(enum paravirt_lazy_mode mode)
 {
         BUG_ON(__get_cpu_var(paravirt_lazy_mode) != mode);
         BUG_ON(preemptible());
@@ -267,17 +267,24 @@ void paravirt_enter_lazy_mmu(void)
 
 void paravirt_leave_lazy_mmu(void)
 {
-        paravirt_leave_lazy(PARAVIRT_LAZY_MMU);
+        leave_lazy(PARAVIRT_LAZY_MMU);
 }
 
 void paravirt_enter_lazy_cpu(void)
 {
+        if (percpu_read(paravirt_lazy_mode) == PARAVIRT_LAZY_MMU) {
+                arch_leave_lazy_mmu_mode();
+                set_thread_flag(TIF_LAZY_MMU_UPDATES);
+        }
         enter_lazy(PARAVIRT_LAZY_CPU);
 }
 
 void paravirt_leave_lazy_cpu(void)
 {
-        paravirt_leave_lazy(PARAVIRT_LAZY_CPU);
+        leave_lazy(PARAVIRT_LAZY_CPU);
+
+        if (test_and_clear_thread_flag(TIF_LAZY_MMU_UPDATES))
+                arch_enter_lazy_mmu_mode();
 }
 
 enum paravirt_lazy_mode paravirt_get_lazy_mode(void)