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SubjectRE: [PATCH v2] KVM: x86: Sync the pending Posted-Interrupts
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> >> This is not what I asked.  You should instead do the check after pi_clear_sn.
> >>
> >
> > I think the SN has been cleared here before test the bitmap.
> > The SN will be set when the vCPU is schedule out. ID:
> > 28b835d60fcc2498e717cf5e6f0c3691c24546f7
> > But SN will be cleared when sched in.
> >
> > Another place is when vCPU run out of the vcpu_run() function:
> > kvm_arch_vcpu_ioctl_run()
> > vcpu_load(vcpu); -> kvm_arch_vcpu_load -> vmx_vcpu_load -> vmx_vcpu_pi_load -> new.sn = 0;
> > vcpu_run(vcpu);
> > for(;;)
> > vcpu_put(vcpu); -> kvm_arch_vcpu_put -> vmx_vcpu_put ->
> > vmx_vcpu_pi_put -> pi_set_sn() But SN will be cleared in vcpu_load()
> > before back to vcpu_run()
>
> Yes, but you're changing the wrong path. The patch is affecting _all_ vmentries, not just those after PID.SN has been cleared.
>
> As I mentioned in the previous email, KVM relies on the SDM's invariant that ON where PID.ON=1 whenever PID.PIR!=0. Invariants are your
> best friend when dealing with complicated multi-processor code so I don't want to change that.
>
> It's the VT-d pi_clear_sn path that I want to be changed, because it's VT-d and specifically SN that complicates the very simple definition in
> the SDM. By modifying the pi_clear_sn path, you ensure the invariant is respected and everyone is happy.

Hi Paolo,
How about like this:

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 820a03b..dfc5e3d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1219,6 +1219,9 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
new.ndst = (dest << 8) & 0xFF00;

new.sn = 0;
+
+ if (!bitmap_empty((unsigned long *)new.pir, NR_VECTORS))
+ new.on = 1;
} while (cmpxchg64(&pi_desc->control, old.control,
new.control) != old.control);
}

Thanks,
Luwei Kang
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