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SubjectRe: [PATCH RFC V10 16/18] kvm hypervisor : Simplify kvm_for_each_vcpu with kvm_irq_delivery_to_apic
On 07/15/2013 09:16 PM, Gleb Natapov wrote:
> On Mon, Jul 15, 2013 at 09:06:13PM +0530, Raghavendra K T wrote:
>> On 07/14/2013 06:54 PM, Gleb Natapov wrote:
>>> On Mon, Jun 24, 2013 at 06:13:53PM +0530, Raghavendra K T wrote:
>>>> Simplify kvm_for_each_vcpu with kvm_irq_delivery_to_apic
>>>>
>>>> From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
>>>>
>>>> Note that we are using APIC_DM_REMRD which has reserved usage.
>>>> In future if APIC_DM_REMRD usage is standardized, then we should
>>>> find some other way or go back to old method.
>>>>
>>>> Suggested-by: Gleb Natapov <gleb@redhat.com>
>>>> Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
>>>> ---
>>>> arch/x86/kvm/lapic.c | 5 ++++-
>>>> arch/x86/kvm/x86.c | 25 ++++++-------------------
>>>> 2 files changed, 10 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>>>> index e1adbb4..3f5f82e 100644
>>>> --- a/arch/x86/kvm/lapic.c
>>>> +++ b/arch/x86/kvm/lapic.c
>>>> @@ -706,7 +706,10 @@ out:
>>>> break;
>>>>
>>>> case APIC_DM_REMRD:
>>>> - apic_debug("Ignoring delivery mode 3\n");
>>>> + result = 1;
>>>> + vcpu->arch.pv.pv_unhalted = 1;
>>>> + kvm_make_request(KVM_REQ_EVENT, vcpu);
>>>> + kvm_vcpu_kick(vcpu);
>>>> break;
>>>>
>>>> case APIC_DM_SMI:
>>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>>> index 92a9932..b963c86 100644
>>>> --- a/arch/x86/kvm/x86.c
>>>> +++ b/arch/x86/kvm/x86.c
>>>> @@ -5456,27 +5456,14 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>>>> */
>>>> static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
>>>> {
>>>> - struct kvm_vcpu *vcpu = NULL;
>>>> - int i;
>>>> + struct kvm_lapic_irq lapic_irq;
>>>>
>>>> - kvm_for_each_vcpu(i, vcpu, kvm) {
>>>> - if (!kvm_apic_present(vcpu))
>>>> - continue;
>>>> + lapic_irq.shorthand = 0;
>>>> + lapic_irq.dest_mode = 0;
>>>> + lapic_irq.dest_id = apicid;
>>>>
>>>> - if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
>>>> - break;
>>>> - }
>>>> - if (vcpu) {
>>>> - /*
>>>> - * Setting unhalt flag here can result in spurious runnable
>>>> - * state when unhalt reset does not happen in vcpu_block.
>>>> - * But that is harmless since that should soon result in halt.
>>>> - */
>>>> - vcpu->arch.pv.pv_unhalted = true;
>>>> - /* We need everybody see unhalt before vcpu unblocks */
>>>> - smp_wmb();
>>>> - kvm_vcpu_kick(vcpu);
>>>> - }
>>>> + lapic_irq.delivery_mode = APIC_DM_REMRD;
>>> Need to make sure that delivery_mode cannot be set to APIC_DM_REMRD
>> >from MSI/IOAPIC/IPI path.
>>
>> I Gleb,
>> I need your help here since I do not know much about apic.
>>
>> so are you saying explicitly checking that, kvm_set_msi_irq,
>> apic_send_ipi, native_setup_ioapic_entry, does not have
>> APIC_DM_REMRD as delivery_mode set?
>>
> Yes, but on a second thought what bad can happen if we will not check it?
> If guest configures irq to inject APIC_DM_REMRD interrupt this may
> needlessly wakeup sleeping vcpu and it will try to accrue spinlock
> again, so no correctness problem only performance. If this is the case
> lets leave it as it for now.

Okay.



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