[Xen-devel] [PATCH] x86: vlapic: Clear vector's TMR bit upon acceptance of edge-triggered interrupt to IRR

[Liran Alon <liran.alon@xxxxxxxxxx>]

According to Intel SDM 10.8.4 Interrupt Acceptance for Fixed Interrupts:
"The trigger mode register (TMR) indicates the trigger mode of the
interrupt (see Figure 10-20). Upon acceptance of an interrupt
into the IRR, the corresponding TMR bit is cleared for
edge-triggered interrupts and set for level-triggered interrupts.
If a TMR bit is set when an EOI cycle for its corresponding
interrupt vector is generated, an EOI message is sent to
all I/O APICs."

Before this patch TMR-bit was cleared on LAPIC EOI which is not what
real hardware does. This was also confirmed in KVM upstream commit
a0c9a822bf37 ("KVM: dont clear TMR on EOI").

Behavior after this patch is aligned with both Intel SDM and KVM
implementation.

Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vlapic.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 7387f91fe04e..9fb0066bfff7 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -161,6 +161,8 @@ void vlapic_set_irq(struct vlapic *vlapic, uint8_t vec, 
uint8_t trig)
 
     if ( trig )
         vlapic_set_vector(vec, &vlapic->regs->data[APIC_TMR]);
+    else
+        vlapic_clear_vector(vec, &vlapic->regs->data[APIC_TMR]);
 
     if ( hvm_funcs.update_eoi_exit_bitmap )
         hvm_funcs.update_eoi_exit_bitmap(target, vec, trig);
@@ -461,7 +463,7 @@ void vlapic_handle_EOI(struct vlapic *vlapic, u8 vector)
 {
     struct domain *d = vlapic_domain(vlapic);
 
-    if ( vlapic_test_and_clear_vector(vector, &vlapic->regs->data[APIC_TMR]) )
+    if ( vlapic_test_vector(vector, &vlapic->regs->data[APIC_TMR]) )
         vioapic_update_EOI(d, vector);
 
     hvm_dpci_msi_eoi(d, vector);
-- 
1.9.1


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