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, 6 insertions, 1 deletions

diff --git a/xen/arch/x86/hvm/vpic.c b/xen/arch/x86/hvm/vpic.c
index 81bfac5db7..fea3f68f9e 100644
--- a/xen/arch/x86/hvm/vpic.c
+++ b/xen/arch/x86/hvm/vpic.c
@@ -178,7 +178,7 @@ static void vpic_ioport_write(
     struct hvm_hw_vpic *vpic, uint32_t addr, uint32_t val)
 {
     int priority, cmd, irq;
-    uint8_t mask;
+    uint8_t mask, unmasked = 0;
 
     vpic_lock(vpic);
 
@@ -190,6 +190,7 @@ static void vpic_ioport_write(
             /* Clear edge-sensing logic. */
             vpic->irr &= vpic->elcr;
 
+            unmasked = vpic->imr;
             /* No interrupts masked or in service. */
             vpic->imr = vpic->isr = 0;
 
@@ -268,6 +269,7 @@ static void vpic_ioport_write(
         {
         case 0:
             /* OCW1 */
+            unmasked = vpic->imr & (~val);
             vpic->imr = val;
             break;
         case 1:
@@ -295,6 +297,9 @@ static void vpic_ioport_write(
     vpic_update_int_output(vpic);
 
     vpic_unlock(vpic);
+
+    if ( unmasked )
+        pt_may_unmask_irq(vpic_domain(vpic), NULL);
 }
 
 static uint32_t vpic_ioport_read(struct hvm_hw_vpic *vpic, uint32_t addr)