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>

9 files changed, 42 insertions, 18 deletions

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 7b28abac323f..58d2481b01a6 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -1418,7 +1418,6 @@ void paravirt_enter_lazy_cpu(void);
 void paravirt_leave_lazy_cpu(void);
 void paravirt_enter_lazy_mmu(void);
 void paravirt_leave_lazy_mmu(void);
-void paravirt_leave_lazy(enum paravirt_lazy_mode mode);
 
 #define  __HAVE_ARCH_START_CONTEXT_SWITCH
 static inline void arch_start_context_switch(void)
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index df9d5f78385e..2f34d643b567 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -94,6 +94,7 @@ struct thread_info {
 #define TIF_FORCED_TF           24      /* true if TF in eflags artificially */
 #define TIF_DEBUGCTLMSR         25      /* uses thread_struct.debugctlmsr */
 #define TIF_DS_AREA_MSR         26      /* uses thread_struct.ds_area_msr */
+#define TIF_LAZY_MMU_UPDATES    27      /* task is updating the mmu lazily */
 
 #define _TIF_SYSCALL_TRACE      (1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME      (1 << TIF_NOTIFY_RESUME)
@@ -115,6 +116,7 @@ struct thread_info {
 #define _TIF_FORCED_TF          (1 << TIF_FORCED_TF)
 #define _TIF_DEBUGCTLMSR        (1 << TIF_DEBUGCTLMSR)
 #define _TIF_DS_AREA_MSR        (1 << TIF_DS_AREA_MSR)
+#define _TIF_LAZY_MMU_UPDATES   (1 << TIF_LAZY_MMU_UPDATES)
 
 /* work to do in syscall_trace_enter() */
 #define _TIF_WORK_SYSCALL_ENTRY \
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 478bca986eca..5d7f6e76b5dc 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -201,7 +201,7 @@ static void kvm_leave_lazy_mmu(void)
         struct kvm_para_state *state = kvm_para_state();
 
         mmu_queue_flush(state);
-        paravirt_leave_lazy(paravirt_get_lazy_mode());
+        paravirt_leave_lazy_mmu();
         state->mode = paravirt_get_lazy_mode();
 }
 
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 5eea9548216b..430a0e30577b 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)
diff --git a/arch/x86/kernel/vmi_32.c b/arch/x86/kernel/vmi_32.c
index 2cc4a90e2cb3..950929c607d3 100644
--- a/arch/x86/kernel/vmi_32.c
+++ b/arch/x86/kernel/vmi_32.c
@@ -473,16 +473,22 @@ static void vmi_enter_lazy_cpu(void)
         vmi_ops.set_lazy_mode(2);
 }
 
+static void vmi_leave_lazy_cpu(void)
+{
+        vmi_ops.set_lazy_mode(0);
+        paravirt_leave_lazy_cpu();
+}
+
 static void vmi_enter_lazy_mmu(void)
 {
         paravirt_enter_lazy_mmu();
         vmi_ops.set_lazy_mode(1);
 }
 
-static void vmi_leave_lazy(void)
+static void vmi_leave_lazy_mmu(void)
 {
-        paravirt_leave_lazy(paravirt_get_lazy_mode());
         vmi_ops.set_lazy_mode(0);
+        paravirt_leave_lazy_mmu();
 }
 
 static inline int __init check_vmi_rom(struct vrom_header *rom)
@@ -718,12 +724,12 @@ static inline int __init activate_vmi(void)
 
         para_wrap(pv_cpu_ops.lazy_mode.enter, vmi_enter_lazy_cpu,
                   set_lazy_mode, SetLazyMode);
-        para_wrap(pv_cpu_ops.lazy_mode.leave, vmi_leave_lazy,
+        para_wrap(pv_cpu_ops.lazy_mode.leave, vmi_leave_lazy_cpu,
                   set_lazy_mode, SetLazyMode);
 
         para_wrap(pv_mmu_ops.lazy_mode.enter, vmi_enter_lazy_mmu,
                   set_lazy_mode, SetLazyMode);
-        para_wrap(pv_mmu_ops.lazy_mode.leave, vmi_leave_lazy,
+        para_wrap(pv_mmu_ops.lazy_mode.leave, vmi_leave_lazy_mmu,
                   set_lazy_mode, SetLazyMode);
 
         /* user and kernel flush are just handled with different flags to FlushTLB */
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 9fe4ddaa8f6f..41a5562e710e 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -147,10 +147,16 @@ static void lazy_hcall(unsigned long call,
 
 /* When lazy mode is turned off reset the per-cpu lazy mode variable and then
  * issue the do-nothing hypercall to flush any stored calls. */
-static void lguest_leave_lazy_mode(void)
+static void lguest_leave_lazy_mmu_mode(void)
 {
-        paravirt_leave_lazy(paravirt_get_lazy_mode());
         hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
+        paravirt_leave_lazy_mmu();
+}
+
+static void lguest_leave_lazy_cpu_mode(void)
+{
+        hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0);
+        paravirt_leave_lazy_cpu();
 }
 
 /*G:033
@@ -1026,7 +1032,7 @@ __init void lguest_init(void)
         pv_cpu_ops.write_idt_entry = lguest_write_idt_entry;
         pv_cpu_ops.wbinvd = lguest_wbinvd;
         pv_cpu_ops.lazy_mode.enter = paravirt_enter_lazy_cpu;
-        pv_cpu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
+        pv_cpu_ops.lazy_mode.leave = lguest_leave_lazy_cpu_mode;
 
         /* pagetable management */
         pv_mmu_ops.write_cr3 = lguest_write_cr3;
@@ -1039,7 +1045,7 @@ __init void lguest_init(void)
         pv_mmu_ops.read_cr2 = lguest_read_cr2;
         pv_mmu_ops.read_cr3 = lguest_read_cr3;
         pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
-        pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
+        pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mmu_mode;
 
 #ifdef CONFIG_X86_LOCAL_APIC
         /* apic read/write intercepts */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 82cd39a6cbd3..f586e63b9a63 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -203,10 +203,10 @@ static unsigned long xen_get_debugreg(int reg)
         return HYPERVISOR_get_debugreg(reg);
 }
 
-void xen_leave_lazy(void)
+static void xen_leave_lazy_cpu(void)
 {
-        paravirt_leave_lazy(paravirt_get_lazy_mode());
         xen_mc_flush();
+        paravirt_leave_lazy_cpu();
 }
 
 static unsigned long xen_store_tr(void)
@@ -819,7 +819,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initdata = {
 
         .lazy_mode = {
                 .enter = paravirt_enter_lazy_cpu,
-                .leave = xen_leave_lazy,
+                .leave = xen_leave_lazy_cpu,
         },
 };
 
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 6b98f87232ac..f5f8faa4f76c 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1816,6 +1816,11 @@ __init void xen_post_allocator_init(void)
         xen_mark_init_mm_pinned();
 }
 
+static void xen_leave_lazy_mmu(void)
+{
+        xen_mc_flush();
+        paravirt_leave_lazy_mmu();
+}
 
 const struct pv_mmu_ops xen_mmu_ops __initdata = {
         .pagetable_setup_start = xen_pagetable_setup_start,
@@ -1891,7 +1896,7 @@ const struct pv_mmu_ops xen_mmu_ops __initdata = {
 
         .lazy_mode = {
                 .enter = paravirt_enter_lazy_mmu,
-                .leave = xen_leave_lazy,
+                .leave = xen_leave_lazy_mmu,
         },
 
         .set_fixmap = xen_set_fixmap,
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 2f5ef2632ea2..f897cdffccb6 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -30,7 +30,6 @@ pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn);
 void xen_ident_map_ISA(void);
 void xen_reserve_top(void);
 
-void xen_leave_lazy(void);
 void xen_post_allocator_init(void);
 
 char * __init xen_memory_setup(void);