Re: [PATCH RFC V4 4/5] kvm : pv-ticketlocks support for linux guests running on KVM hypervisor

Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> · Wed, 25 Jan 2012 00:31:45 +0530

On 01/18/2012 12:27 AM, Raghavendra K T wrote:

On 01/17/2012 04:32 PM, Marcelo Tosatti wrote:

On Sat, Jan 14, 2012 at 11:56:46PM +0530, Raghavendra K T wrote:

[...]

+ || (vcpu->requests& ~(1UL<<KVM_REQ_PVLOCK_KICK))
+ || need_resched() || signal_pending(current)) {
vcpu->mode = OUTSIDE_GUEST_MODE;
smp_wmb();
local_irq_enable();
@@ -6711,6 +6712,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
!vcpu->arch.apf.halted)
|| !list_empty_careful(&vcpu->async_pf.done)
|| vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED
+ || kvm_check_request(KVM_REQ_PVLOCK_KICK, vcpu)


The bit should only be read here (kvm_arch_vcpu_runnable), but cleared
on vcpu entry (along with the other kvm_check_request processing).


[...]


I had tried alternative approach earlier, I think that is closer
to your expectation.

where
- flag is read in kvm_arch_vcpu_runnable
- flag cleared in vcpu entry along with others.

But it needs per vcpu flag to remember that pv_unhalted while clearing
the flag in vcpu enter [ patch below ]. Could not find third alternative
though.

[...]

do you think having pv_unhalt flag in below patch cause problem to
live migration still? (vcpu->request bit is retained as is) OR do we
have to have KVM_GET_MP_STATE changes also with below patch you
mentioned earlier.



Avi, Marcello, Please let me know, any comments you have on how should
it look like in next version?
Should I get rid of KVM_REQ_PVLOCK_KICK bit in vcpu->request and have
only pv_unahlt flag as below and also add MSR as suggested?


---8<---

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c38efd7..1bf8fa8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5684,6 +5717,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
r = 1;
goto out;
}
+ if (kvm_check_request(KVM_REQ_PVKICK, vcpu)) {
+ vcpu->pv_unhalted = 1;
+ r = 1;
+ goto out;
+ }
if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu))
record_steal_time(vcpu);
if (kvm_check_request(KVM_REQ_NMI, vcpu))
@@ -6683,6 +6720,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
!vcpu->arch.apf.halted)
|| !list_empty_careful(&vcpu->async_pf.done)
|| vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED
+ || (kvm_test_request(KVM_REQ_PVKICK, vcpu) || vcpu->pv_unhalted)
|| atomic_read(&vcpu->arch.nmi_queued) ||
(kvm_arch_interrupt_allowed(vcpu) &&
kvm_cpu_has_interrupt(vcpu));
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d526231..a48e0f2 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -154,6 +155,8 @@ struct kvm_vcpu {
#endif

struct kvm_vcpu_arch arch;
+
+ int pv_unhalted;
};

static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
@@ -770,5 +773,12 @@ static inline bool kvm_check_request(int req,
struct kvm_vcpu *vcpu)
}
}

+static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
+{
+ if (test_bit(req, &vcpu->requests))
+ return true;
+ else
+ return false;
+}
#endif

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d9cfb78..55c44a2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -226,6 +226,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm
*kvm, unsigned id)
vcpu->kvm = kvm;
vcpu->vcpu_id = id;
vcpu->pid = NULL;
+ vcpu->pv_unhalted = 0;
init_waitqueue_head(&vcpu->wq);
kvm_async_pf_vcpu_init(vcpu);

@@ -1509,11 +1510,12 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
void kvm_vcpu_block(struct kvm_vcpu *vcpu)
{
DEFINE_WAIT(wait);
for (;;) {
prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);

if (kvm_arch_vcpu_runnable(vcpu)) {
+ vcpu->pv_unhalted = 0;
kvm_make_request(KVM_REQ_UNHALT, vcpu);
break;
}



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