x86 hvm: suspend platform timer emulation while its IRQ is masked

This patch gets rid of a timer which IRQ is masked from vcpu's timer
list. It reduces the overhead of VM EXIT and context switch of vm.

Also fixes a potential bug.
(1) VCPU#0: mask the IRQ of a timer. (ex. vioapic.redir[2].mask=1)
(2) VCPU#1: pt_timer_fn() is invoked by expiration of the timer.
(3) VCPU#1: pt_update_irq() is called but does nothing by
pt_irq_masked()==1.
(4) VCPU#1: sleep by halt.
(5) VCPU#0: unmask the IRQ of the timer.
After that, no one wakes up the VCPU#1.

IRQ of ISA is masked by:
 - PIC's IMR
 - IOAPIC's redir[0]
 - IOAPIC's redir[N].mask
 - LAPIC's LVT0
 - LAPIC enabled/disabled

IRQ of LAPIC timer is masked by:
 - LAPIC's LVTT
 - LAPIC disabled

When above stuffs are changed, the corresponding vcpu is kicked and
suspended timer emulation is resumed.

In addition, a small bug fix in pt_adjust_global_vcpu_target().

Signed-off-by: Kouya Shimura <kouya@jp.fujitsu.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index b915609d36..603a9200ab 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -624,7 +624,10 @@ static int vlapic_write(struct vcpu *v, unsigned long address,
             }
         }
         else
+        {
             vlapic->hw.disabled &= ~VLAPIC_SW_DISABLED;
+            pt_may_unmask_irq(vlapic_domain(vlapic), &vlapic->pt);
+        }
         break;
 
     case APIC_ESR:
@@ -654,7 +657,12 @@ static int vlapic_write(struct vcpu *v, unsigned long address,
         val &= vlapic_lvt_mask[(offset - APIC_LVTT) >> 4];
         vlapic_set_reg(vlapic, offset, val);
         if ( offset == APIC_LVT0 )
+        {
             vlapic_adjust_i8259_target(v->domain);
+            pt_may_unmask_irq(v->domain, NULL);
+        }
+        if ( (offset == APIC_LVTT) && !(val & APIC_LVT_MASKED) )
+            pt_may_unmask_irq(NULL, &vlapic->pt);
         break;
 
     case APIC_TMICT:
@@ -719,10 +727,12 @@ void vlapic_msr_set(struct vlapic *vlapic, uint64_t value)
         {
             vlapic_reset(vlapic);
             vlapic->hw.disabled &= ~VLAPIC_HW_DISABLED;
+            pt_may_unmask_irq(vlapic_domain(vlapic), &vlapic->pt);
         }
         else
         {
             vlapic->hw.disabled |= VLAPIC_HW_DISABLED;
+            pt_may_unmask_irq(vlapic_domain(vlapic), NULL);
         }
     }