[PATCH 1/2] KVM: provide irq_unsafe kvm_guest_{enter|exit}

Christian Borntraeger
2015-04-30T11:43:30Z

Several kvm architectures disable interrupts before kvm_guest_enter.
kvm_guest_enter then uses local_irq_save/restore to disable interrupts
again or for the first time. Lets provide underscore versions of
kvm_guest_{enter|exit} that assume being called locked.
kvm_guest_enter now disables interrupts for the full function and
thus we can remove the check for preemptible.

This patch then adopts s390/kvm to use local_irq_disable/enable calls
which are slighty cheaper that local_irq_save/restore and call these
new functions.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
arch/s390/kvm/kvm-s390.c | 10 ++++++----
include/linux/kvm_host.h | 27 ++++++++++++++++++---------
2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 46f37df..c25d4e5 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2010,12 +2010,14 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
* As PF_VCPU will be used in fault handler, between
* guest_enter and guest_exit should be no uaccess.
*/
- preempt_disable();
- kvm_guest_enter();
- preempt_enable();
+ local_irq_disable();
+ __kvm_guest_enter();
+ local_irq_enable();
exit_reason = sie64a(vcpu->arch.sie_block,
vcpu->run->s.regs.gprs);
- kvm_guest_exit();
+ local_irq_disable();
+ __kvm_guest_exit();
+ local_irq_enable();
vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);

rc = vcpu_post_run(vcpu, exit_reason);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d12b210..2d3b3ce 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -749,16 +749,10 @@ static inline void kvm_iommu_unmap_pages(struct kvm *kvm,
}
#endif

-static inline void kvm_guest_enter(void)
+/* must be called with irqs disabled */
+static inline void __kvm_guest_enter(void)
{
- unsigned long flags;
-
- BUG_ON(preemptible());
-
- local_irq_save(flags);
guest_enter();
- local_irq_restore(flags);
-
/* KVM does not hold any references to rcu protected data when it
* switches CPU into a guest mode. In fact switching to a guest mode
* is very similar to exiting to userspace from rcu point of view. In
@@ -769,12 +763,27 @@ static inline void kvm_guest_enter(void)
rcu_virt_note_context_switch(smp_processor_id());
}

+/* must be called with irqs disabled */
+static inline void __kvm_guest_exit(void)
+{
+ guest_exit();
+}
+
+static inline void kvm_guest_enter(void)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ __kvm_guest_enter();
+ local_irq_restore(flags);
+}
+
static inline void kvm_guest_exit(void)
{
unsigned long flags;

local_irq_save(flags);
- guest_exit();
+ __kvm_guest_exit();
local_irq_restore(flags);
}

--
2.3.0