[xen staging] x86/hvm: fix ISA IRQ 0 handling when set as lowest priority mode in IO APIC

[patchbot@xxxxxxx]

commit dc036ab9d506b997777c7656d9e6e4fa32bc582e
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Mon Jul 27 19:05:37 2020 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Jul 28 19:33:28 2020 +0100

    x86/hvm: fix ISA IRQ 0 handling when set as lowest priority mode in IO APIC
    
    Lowest priority destination mode does allow the vIO APIC code to
    select a vCPU to inject the interrupt to, but the selected vCPU must
    be part of the possible destinations configured for such IO APIC pin.
    
    Fix the code in order to only force vCPU 0 if it's part of the
    listed destinations.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vioapic.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/hvm/vioapic.c b/xen/arch/x86/hvm/vioapic.c
index 123191db75..67d4a6237f 100644
--- a/xen/arch/x86/hvm/vioapic.c
+++ b/xen/arch/x86/hvm/vioapic.c
@@ -415,12 +415,14 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, 
unsigned int pin)
     case dest_LowestPrio:
     {
 #ifdef IRQ0_SPECIAL_ROUTING
-        /* Force round-robin to pick VCPU 0 */
-        if ( (irq == hvm_isa_irq_to_gsi(0)) && pt_active(&d->arch.vpit.pt0) )
-        {
-            v = d->vcpu ? d->vcpu[0] : NULL;
-            target = v ? vcpu_vlapic(v) : NULL;
-        }
+        struct vlapic *lapic0 = vcpu_vlapic(d->vcpu[0]);
+
+        /* Force to pick vCPU 0 if part of the destination list */
+        if ( (irq == hvm_isa_irq_to_gsi(0)) && pt_active(&d->arch.vpit.pt0) &&
+             vlapic_match_dest(lapic0, NULL, 0, dest, dest_mode) &&
+             /* Mimic the vlapic_enabled check found in vlapic_lowest_prio. */
+             vlapic_enabled(lapic0) )
+            target = lapic0;
         else
 #endif
             target = vlapic_lowest_prio(d, NULL, 0, dest, dest_mode);
--
generated by git-patchbot for /home/xen/git/xen.git#staging