Avi Kivity wrote:
Applied, but I note that entering the guest with any lock held is
problematic, as the guest may spend an arbitrary amount of time in guest
mode. Really, entering the guest is almost exactly like exiting to
userspace.
Hi Avi,
I had a look at this and reworked the locking some, so we don't hold
the slots_lock when entering the guest.
How does this look? Xiantao any thoughts of whether it's unsafe to call
kvm_vcpu_post_transition without holding that semaphore? I believe it
should be fine.
I am still seeing issues where the host can get a lock timeout when
running large guests, but the situation seems to be better with this
patch applied.
Cheers,
Jes
Reorder locking to avoid holding the slots_lock when entering
the guest.
Signed-off-by: Jes Sorensen <jes@xxxxxxx>
---
arch/ia64/kvm/kvm-ia64.c | 64 ++++++++++++++++++++++++-----------------------
1 file changed, 33 insertions(+), 31 deletions(-)
Index: linux-2.6.git/arch/ia64/kvm/kvm-ia64.c
===================================================================
--- linux-2.6.git.orig/arch/ia64/kvm/kvm-ia64.c
+++ linux-2.6.git/arch/ia64/kvm/kvm-ia64.c
@@ -580,34 +580,22 @@
vti_set_rr6(vcpu->arch.vmm_rr);
return kvm_insert_vmm_mapping(vcpu);
}
+
static void kvm_vcpu_post_transition(struct kvm_vcpu *vcpu)
{
kvm_purge_vmm_mapping(vcpu);
vti_set_rr6(vcpu->arch.host_rr6);
}
-static int vti_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+static int __vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
{
union context *host_ctx, *guest_ctx;
int r;
- /*Get host and guest context with guest address space.*/
- host_ctx = kvm_get_host_context(vcpu);
- guest_ctx = kvm_get_guest_context(vcpu);
-
- r = kvm_vcpu_pre_transition(vcpu);
- if (r < 0)
- goto out;
- kvm_vmm_info->tramp_entry(host_ctx, guest_ctx);
- kvm_vcpu_post_transition(vcpu);
- r = 0;
-out:
- return r;
-}
-
-static int __vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
-{
- int r;
+ /*
+ * down_read() may sleep and return with interrupts enabled
+ */
+ down_read(&vcpu->kvm->slots_lock);
again:
if (signal_pending(current)) {
@@ -616,23 +604,28 @@
goto out;
}
- /*
- * down_read() may sleep and return with interrupts enabled
- */
- down_read(&vcpu->kvm->slots_lock);
-
preempt_disable();
local_irq_disable();
+ /*Get host and guest context with guest address space.*/
+ host_ctx = kvm_get_host_context(vcpu);
+ guest_ctx = kvm_get_guest_context(vcpu);
+
vcpu->guest_mode = 1;
+
+ r = kvm_vcpu_pre_transition(vcpu);
+ if (r < 0)
+ goto vcpu_run_fail;
+
+ up_read(&vcpu->kvm->slots_lock);
kvm_guest_enter();
- r = vti_vcpu_run(vcpu, kvm_run);
- if (r < 0) {
- local_irq_enable();
- preempt_enable();
- kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY;
- goto out;
- }
+
+ /*
+ * Transition to the guest
+ */
+ kvm_vmm_info->tramp_entry(host_ctx, guest_ctx);
+
+ kvm_vcpu_post_transition(vcpu);
vcpu->arch.launched = 1;
vcpu->guest_mode = 0;
@@ -646,9 +639,10 @@
*/
barrier();
kvm_guest_exit();
- up_read(&vcpu->kvm->slots_lock);
preempt_enable();
+ down_read(&vcpu->kvm->slots_lock);
+
r = kvm_handle_exit(kvm_run, vcpu);
if (r > 0) {
@@ -657,12 +651,20 @@
}
out:
+ up_read(&vcpu->kvm->slots_lock);
if (r > 0) {
kvm_resched(vcpu);
+ down_read(&vcpu->kvm->slots_lock);
goto again;
}
return r;
+
+vcpu_run_fail:
+ local_irq_enable();
+ preempt_enable();
+ kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY;
+ goto out;
}
static void kvm_set_mmio_data(struct kvm_vcpu *vcpu)
