[Xen-devel] [PATCH 6/9] x86/paravirt: allow preemption with lazy mmu mode

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

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

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 arch/x86/kernel/paravirt.c |    7 ++++---
 arch/x86/xen/mmu.c         |    8 +-------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 554dadd..1a81ce9 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -248,7 +248,6 @@ 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;
 }
@@ -256,7 +255,6 @@ 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;
 }
@@ -273,6 +271,8 @@ void paravirt_leave_lazy_mmu(void)
 
 void paravirt_enter_lazy_cpu(void)
 {
+       BUG_ON(preemptible());
+
        if (percpu_read(paravirt_lazy_mode) == PARAVIRT_LAZY_MMU) {
                arch_leave_lazy_mmu_mode();
                set_thread_flag(TIF_LAZY_MMU_UPDATES);
@@ -282,6 +282,8 @@ void paravirt_enter_lazy_cpu(void)
 
 void paravirt_leave_lazy_cpu(void)
 {
+       BUG_ON(preemptible());
+
        leave_lazy(PARAVIRT_LAZY_CPU);
 
        if (test_and_clear_thread_flag(TIF_LAZY_MMU_UPDATES))
@@ -301,7 +303,6 @@ 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 2669c58..92c6463 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -412,10 +412,6 @@ 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);
@@ -436,9 +432,7 @@ 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,
-- 
1.6.0.6


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