x86/paravirt: allow preemption with lazy mmu mode

Impact: remove obsolete checks, simplification

Lift restrictions on preemption with lazy mmu mode, as it is now allowed.

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

2 files changed, 5 insertions, 10 deletions

diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index cf1437503ba..bf2e86eee80 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -247,7 +247,6 @@ static DEFINE_PER_CPU(enum paravirt_lazy_mode, paravirt_lazy_mode) = PARAVIRT_LA
 static inline void enter_lazy(enum paravirt_lazy_mode mode)
 {
         BUG_ON(__get_cpu_var(paravirt_lazy_mode) != PARAVIRT_LAZY_NONE);
-        BUG_ON(preemptible());
 
         __get_cpu_var(paravirt_lazy_mode) = mode;
 }
@@ -255,7 +254,6 @@ static inline void enter_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());
 
         __get_cpu_var(paravirt_lazy_mode) = PARAVIRT_LAZY_NONE;
 }
@@ -272,6 +270,8 @@ void paravirt_leave_lazy_mmu(void)
 
 void paravirt_start_context_switch(struct task_struct *prev)
 {
+        BUG_ON(preemptible());
+
         if (percpu_read(paravirt_lazy_mode) == PARAVIRT_LAZY_MMU) {
                 arch_leave_lazy_mmu_mode();
                 set_ti_thread_flag(task_thread_info(prev), TIF_LAZY_MMU_UPDATES);
@@ -281,6 +281,8 @@ void paravirt_start_context_switch(struct task_struct *prev)
 
 void paravirt_end_context_switch(struct task_struct *next)
 {
+        BUG_ON(preemptible());
+
         leave_lazy(PARAVIRT_LAZY_CPU);
 
         if (test_and_clear_ti_thread_flag(task_thread_info(next), TIF_LAZY_MMU_UPDATES))
@@ -300,7 +302,6 @@ void arch_flush_lazy_mmu_mode(void)
         preempt_disable();
 
         if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
-                WARN_ON(preempt_count() == 1);
                 arch_leave_lazy_mmu_mode();
                 arch_enter_lazy_mmu_mode();
         }
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index f5f8faa4f76..3f2d0fe5e6a 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -419,10 +419,6 @@ void set_pte_mfn(unsigned long vaddr, unsigned long mfn, pgprot_t flags)
 void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
                     pte_t *ptep, pte_t pteval)
 {
-        /* updates to init_mm may be done without lock */
-        if (mm == &init_mm)
-                preempt_disable();
-
         ADD_STATS(set_pte_at, 1);
 //      ADD_STATS(set_pte_at_pinned, xen_page_pinned(ptep));
         ADD_STATS(set_pte_at_current, mm == current->mm);
@@ -443,9 +439,7 @@ void xen_set_pte_at(struct mm_struct *mm, unsigned long addr,
         }
         xen_set_pte(ptep, pteval);
 
-out:
-        if (mm == &init_mm)
-                preempt_enable();
+out:    return;
 }
 
 pte_t xen_ptep_modify_prot_start(struct mm_struct *mm,