On Thu, 2021-10-28 at 14:28 +0300, Maxim Levitsky wrote:

On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote:

quoted

Hoist the CPU => APIC ID conversion for the Posted Interrupt descriptor
out of the loop to write the descriptor, preemption is disabled so the
CPU won't change, and if the APIC ID changes KVM has bigger problems.

No functional change intended.

Is preemption always disabled in vmx_vcpu_pi_load? vmx_vcpu_pi_load is called from vmx_vcpu_load,
which is called indirectly from vcpu_load which is called from many ioctls,
which userspace does. In these places I don't think that preemption is disabled.

You can disregard this, I missed the fact that we have 'int cpu = get_cpu();'
which disables preemption in 'vcpu_load'

Thus,

Reviewed-by: Maxim Levitsky <redacted>


Best regards,
	Maxim Levitsky

Best regards,
	Maxim Levitsky

quoted

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/posted_intr.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index fea343dcc011..2b2206339174 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c

@@ -51,17 +51,15 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
 		goto after_clear_sn;
 	}
 
-	/* The full case.  */
+	/* The full case.  Set the new destination and clear SN. */
+	dest = cpu_physical_id(cpu);
+	if (!x2apic_mode)
+		dest = (dest << 8) & 0xFF00;
+
 	do {
 		old.control = new.control = READ_ONCE(pi_desc->control);
 
-		dest = cpu_physical_id(cpu);
-
-		if (x2apic_mode)
-			new.ndst = dest;
-		else
-			new.ndst = (dest << 8) & 0xFF00;
-
+		new.ndst = dest;
 		new.sn = 0;
 	} while (cmpxchg64(&pi_desc->control, old.control,
 			   new.control) != old.control);

@@ -103,15 +101,14 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
 	WARN(pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR,
 	     "Wakeup handler not enabled while the vCPU was blocking");
 
+	dest = cpu_physical_id(vcpu->cpu);
+	if (!x2apic_mode)
+		dest = (dest << 8) & 0xFF00;
+
 	do {
 		old.control = new.control = READ_ONCE(pi_desc->control);
 
-		dest = cpu_physical_id(vcpu->cpu);
-
-		if (x2apic_mode)
-			new.ndst = dest;
-		else
-			new.ndst = (dest << 8) & 0xFF00;
+		new.ndst = dest;
 
 		/* set 'NV' to 'notification vector' */
 		new.nv = POSTED_INTR_VECTOR;