x86/HVM: RTC code must be in line with WAET flags passed by hvmloader

With hvmloader telling the guest that it may skip REG_C reads during
the processing of RTC interrupts, the emulation code must not depend
upon these reads to occur. Introduce two modes of operation for the
emulation code, and short of a HVM parameter (too late to be
introduced for 4.3) hard code the mode determination to always assume
that Windows-conforming one for the time being.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Roger Pau Monné <roger.pau@citrix.com> (FreeBSD guest)

2 files changed, 23 insertions, 8 deletions

diff --git a/tools/firmware/hvmloader/acpi/static_tables.c b/tools/firmware/hvmloader/acpi/static_tables.c
index f98c8d2d10..323ae3124c 100644
--- a/tools/firmware/hvmloader/acpi/static_tables.c
+++ b/tools/firmware/hvmloader/acpi/static_tables.c
@@ -136,11 +136,15 @@ struct acpi_20_rsdp Rsdp = {
     .length    = sizeof(struct acpi_20_rsdp)
 };
 
-#define ACPI_WAET_RTC_GOOD      0x00000001
-#define ACPI_WAET_PM_TIMER_GOOD 0x00000002
+#define ACPI_WAET_RTC_NO_ACK        (1<<0) /* RTC requires no int acknowledge */
+#define ACPI_WAET_TIMER_ONE_READ    (1<<1) /* PM timer requires only one read */
 
-#define ACPI_WAET_FLAGS (ACPI_WAET_RTC_GOOD | \
-                         ACPI_WAET_PM_TIMER_GOOD)
+/*
+ * The state of the RTC flag getting passed to the guest must be in
+ * sync with the mode selection in the hypervisor RTC emulation code.
+ */
+#define ACPI_WAET_FLAGS (ACPI_WAET_RTC_NO_ACK | \
+                         ACPI_WAET_TIMER_ONE_READ)
 
 struct acpi_20_waet Waet = {
     .header = {
diff --git a/xen/arch/x86/hvm/rtc.c b/xen/arch/x86/hvm/rtc.c
index 77b380f287..d1a6848fbb 100644
--- a/xen/arch/x86/hvm/rtc.c
+++ b/xen/arch/x86/hvm/rtc.c
@@ -45,6 +45,15 @@
 #define epoch_year     1900
 #define get_year(x)    (x + epoch_year)
 
+enum rtc_mode {
+   rtc_mode_no_ack,
+   rtc_mode_strict
+};
+
+/* This must be in sync with how hvmloader sets the ACPI WAET flags. */
+#define mode_is(d, m) ((void)(d), rtc_mode_##m == rtc_mode_no_ack)
+#define rtc_mode_is(s, m) mode_is(vrtc_domain(s), m)
+
 static void rtc_copy_date(RTCState *s);
 static void rtc_set_time(RTCState *s);
 static inline int from_bcd(RTCState *s, int a);
@@ -54,7 +63,7 @@ static void rtc_update_irq(RTCState *s)
 {
     ASSERT(spin_is_locked(&s->lock));
 
-    if ( s->hw.cmos_data[RTC_REG_C] & RTC_IRQF )
+    if ( rtc_mode_is(s, strict) && (s->hw.cmos_data[RTC_REG_C] & RTC_IRQF) )
         return;
 
     /* IRQ is raised if any source is both raised & enabled */
@@ -64,6 +73,8 @@ static void rtc_update_irq(RTCState *s)
         return;
 
     s->hw.cmos_data[RTC_REG_C] |= RTC_IRQF;
+    if ( rtc_mode_is(s, no_ack) )
+        hvm_isa_irq_deassert(vrtc_domain(s), RTC_IRQ);
     hvm_isa_irq_assert(vrtc_domain(s), RTC_IRQ);
 }
 
@@ -73,8 +84,8 @@ bool_t rtc_periodic_interrupt(void *opaque)
     bool_t ret;
 
     spin_lock(&s->lock);
-    ret = !(s->hw.cmos_data[RTC_REG_C] & RTC_IRQF);
-    if ( !(s->hw.cmos_data[RTC_REG_C] & RTC_PF) )
+    ret = rtc_mode_is(s, no_ack) || !(s->hw.cmos_data[RTC_REG_C] & RTC_IRQF);
+    if ( rtc_mode_is(s, no_ack) || !(s->hw.cmos_data[RTC_REG_C] & RTC_PF) )
     {
         s->hw.cmos_data[RTC_REG_C] |= RTC_PF;
         rtc_update_irq(s);
@@ -633,7 +644,7 @@ static uint32_t rtc_ioport_read(RTCState *s, uint32_t addr)
     case RTC_REG_C:
         ret = s->hw.cmos_data[s->hw.cmos_index];
         s->hw.cmos_data[RTC_REG_C] = 0x00;
-        if ( ret & RTC_IRQF )
+        if ( (ret & RTC_IRQF) && !rtc_mode_is(s, no_ack) )
             hvm_isa_irq_deassert(d, RTC_IRQ);
         rtc_update_irq(s);
         check_update_timer(s);