local_irq_disable can be cheaper than local_irq_save, especially
when done only once instead of twice. We can push down the
local_irq_save (and replace it with local_irq_disable) to
save some cycles.
x86, mips and arm already disable the interrupts before calling
kvm_guest_enter. Here we save one local_irq_save/restore pair.
power and s390 are reworked to disable the interrupts before calling
kvm_guest_enter. s390 saves a preempt_disable/enable pair but also
saves some cycles as local_irq_disable/enable can be cheaper than
local_irq_save/restore on some machines.
power should be almost a no-op change (interrupts are disabled
slighty longer).
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
arch/powerpc/kvm/book3s_hv.c | 2 ++
arch/s390/kvm/kvm-s390.c | 4 ++--
include/linux/kvm_host.h | 14 ++++++++------
3 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index de74756..a5f392d 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1779,7 +1779,9 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc)
spin_unlock(&vc->lock);
+ local_irq_disable();
kvm_guest_enter();
+ local_irq_enable();
srcu_idx = srcu_read_lock(&vc->kvm->srcu);
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 46f37df..9f4c954 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2010,9 +2010,9 @@ 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();
+ local_irq_disable();
kvm_guest_enter();
- preempt_enable();
+ local_irq_enable();
exit_reason = sie64a(vcpu->arch.sie_block,
vcpu->run->s.regs.gprs);
kvm_guest_exit();
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d12b210..a34bf6ed 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -751,13 +751,15 @@ static inline void kvm_iommu_unmap_pages(struct kvm *kvm,
static inline void kvm_guest_enter(void)
{
- unsigned long flags;
-
- BUG_ON(preemptible());
-
- local_irq_save(flags);
+ /*
+ * guest_enter needs disabled irqs and rcu_virt_note_context_switch
+ * wants disabled preemption. Ensure that the caller has disabled
+ * irqs for kvm_guest_enter. Please note: Some architectures (e.g.
+ * s390) will reenable irqs before entering the guest, but this is
+ * ok. We just need a stable CPU for the accounting itself.
+ */
+ WARN_ON(!irqs_disabled());
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
--
2.3.0
