Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the interrupt is not single-destination

From: Yang Zhang
Date: Wed Jan 20 2016 - 22:34:49 EST

On 2016/1/21 11:14, Wu, Feng wrote:

-----Original Message-----
From: Yang Zhang [mailto:yang.zhang.wz@xxxxxxxxx]
Sent: Thursday, January 21, 2016 11:06 AM
To: Wu, Feng <feng.wu@xxxxxxxxx>; pbonzini@xxxxxxxxxx;
Cc: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v3 1/4] KVM: Recover IRTE to remapped mode if the
interrupt is not single-destination

On 2016/1/20 9:42, Feng Wu wrote:
When the interrupt is not single destination any more, we need
to change back IRTE to remapped mode explicitly.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
arch/x86/kvm/vmx.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e2951b6..13d14d4 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10764,8 +10764,17 @@ static int vmx_update_pi_irte(struct kvm
*kvm, unsigned int host_irq,

kvm_set_msi_irq(e, &irq);
- if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu))
+ if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
+ /*
+ * Make sure the IRTE is in remapped mode if
+ * we don't handle it in posted mode.
+ */
+ pi_set_sn(vcpu_to_pi_desc(vcpu));
+ ret = irq_set_vcpu_affinity(host_irq, NULL);
+ pi_clear_sn(vcpu_to_pi_desc(vcpu));
+ }

vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
vcpu_info.vector = irq.vector;

I am still feel weird with this change: according the semantic of VT-d
posted interrupt, the interrupt will injected to guest through posted
notification and /proc/interrupts shows the same meaning. But now,
without being aware of user, the interrupt changes to legacy way and it
appears on different entry on /proc/interrupts. It looks weird.

I don't think it has problem here, IMO, this is exactly how it works.
There should be different entry for the interrupts in VT-d PI mode
and leagcy mode.

I am not saying any problem here. Just feel weird. From a normal user's point, he has turned on the VT-d pi and according the semantic of VT-d pi, he should not observe the interrupt through legacy mode, but now he do see it. Maybe print out a message here will be helpful, like what you did for disabled lapic found during irq injection.

For VT-d PI mode, it is delivered by notification event, for legacy mode,
it is delivered by VFIO.


Any comments? Paolo.

best regards

best regards