x86/rtc: provide mediated access to RTC for PVH dom0

Mediated access to the RTC was provided for PVHv1 dom0 using the PV
code paths (guest_io_{write/read}), but those accesses where never
implemented for PVHv2 dom0. This patch provides such mediated accesses
to the RTC for PVH dom0, just like it's provided for a classic PV
dom0.

Pull out some of the RTC logic from guest_io_{read/write} into
specific helpers that can be used by both PV and HVM guests. The
setup of the handlers for PVH is done in rtc_init, which is already
used to initialize the fully emulated RTC.

Without this a Linux PVH dom0 will read garbage when trying to access
the RTC, and one vCPU will be constantly looping in
rtc_timer_do_work.

Note that such issue doesn't happen on domUs because the ACPI
NO_CMOS_RTC flag is set in FADT, which prevents the OS from accessing
the RTC. Also the X86_EMU_RTC flag is not set for PVH dom0, as the
accesses are not emulated but rather forwarded to the physical
hardware.

No functional change expected for classic PV dom0.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Paul Durrant <paul@xen.org>

xen/arch/x86/hvm/rtc.c

@@ -808,12 +808,38 @@ void rtc_reset(struct domain *d)
     s->pt.source = PTSRC_isa;
 }
 
+/* RTC mediator for HVM hardware domain. */
+static int hw_rtc_io(int dir, unsigned int port, unsigned int size,
+                     uint32_t *val)
+{
+    if ( dir == IOREQ_READ )
+        *val = ~0;
+
+    if ( size != 1 )
+    {
+        gdprintk(XENLOG_WARNING, "bad RTC access size (%u)\n", size);
+        return X86EMUL_OKAY;
+    }
+
+    if ( dir == IOREQ_WRITE )
+        rtc_guest_write(port, *val);
+    else
+        *val = rtc_guest_read(port);
+
+    return X86EMUL_OKAY;
+}
+
 void rtc_init(struct domain *d)
 {
     RTCState *s = domain_vrtc(d);
 
     if ( !has_vrtc(d) )
+    {
+        if ( is_hardware_domain(d) )
+            /* Hardware domain gets mediated access to the physical RTC. */
+            register_portio_handler(d, RTC_PORT(0), 2, hw_rtc_io);
         return;
+    }
 
     spin_lock_init(&s->lock);
 

xen/arch/x86/pv/emul-priv-op.c

@@ -280,19 +280,9 @@ static uint32_t guest_io_read(unsigned int port, unsigned int bytes,
         {
             sub_data = pv_pit_handler(port, 0, 0);
         }
-        else if ( port == RTC_PORT(0) )
+        else if ( port == RTC_PORT(0) || port == RTC_PORT(1) )
         {
-            sub_data = currd->arch.cmos_idx;
-        }
-        else if ( (port == RTC_PORT(1)) &&
-                  ioports_access_permitted(currd, RTC_PORT(0), RTC_PORT(1)) )
-        {
-            unsigned long flags;
-
-            spin_lock_irqsave(&rtc_lock, flags);
-            outb(currd->arch.cmos_idx & 0x7f, RTC_PORT(0));
-            sub_data = inb(RTC_PORT(1));
-            spin_unlock_irqrestore(&rtc_lock, flags);
+            sub_data = rtc_guest_read(port);
         }
         else if ( (port == 0xcf8) && (bytes == 4) )
         {
@@ -413,21 +403,9 @@ static void guest_io_write(unsigned int port, unsigned int bytes,
         {
             pv_pit_handler(port, (uint8_t)data, 1);
         }
-        else if ( port == RTC_PORT(0) )
+        else if ( port == RTC_PORT(0) || port == RTC_PORT(1) )
         {
-            currd->arch.cmos_idx = data;
-        }
-        else if ( (port == RTC_PORT(1)) &&
-                  ioports_access_permitted(currd, RTC_PORT(0), RTC_PORT(1)) )
-        {
-            unsigned long flags;
-
-            if ( pv_rtc_handler )
-                pv_rtc_handler(currd->arch.cmos_idx & 0x7f, data);
-            spin_lock_irqsave(&rtc_lock, flags);
-            outb(currd->arch.cmos_idx & 0x7f, RTC_PORT(0));
-            outb(data, RTC_PORT(1));
-            spin_unlock_irqrestore(&rtc_lock, flags);
+            rtc_guest_write(port, data);
         }
         else if ( (port == 0xcf8) && (bytes == 4) )
         {

xen/arch/x86/time.c

@@ -27,6 +27,7 @@
 #include <xen/keyhandler.h>
 #include <xen/guest_access.h>
 #include <asm/io.h>
+#include <asm/iocap.h>
 #include <asm/msr.h>
 #include <asm/mpspec.h>
 #include <asm/processor.h>
@@ -1110,6 +1111,70 @@ static unsigned long get_cmos_time(void)
     return mktime(rtc.year, rtc.mon, rtc.day, rtc.hour, rtc.min, rtc.sec);
 }
 
+/* Helpers for guest accesses to the physical RTC. */
+unsigned int rtc_guest_read(unsigned int port)
+{
+    const struct domain *currd = current->domain;
+    unsigned long flags;
+    unsigned int data = ~0;
+
+    switch ( port )
+    {
+    case RTC_PORT(0):
+        /*
+         * All PV domains (and PVH dom0) are allowed to read the latched value
+         * of the first RTC port, as there's no access to the physical IO
+         * ports.
+         */
+        data = currd->arch.cmos_idx;
+        break;
+
+    case RTC_PORT(1):
+        if ( !ioports_access_permitted(currd, RTC_PORT(0), RTC_PORT(1)) )
+            break;
+        spin_lock_irqsave(&rtc_lock, flags);
+        outb(currd->arch.cmos_idx & 0x7f, RTC_PORT(0));
+        data = inb(RTC_PORT(1));
+        spin_unlock_irqrestore(&rtc_lock, flags);
+        break;
+
+    default:
+        ASSERT_UNREACHABLE();
+    }
+
+    return data;
+}
+
+void rtc_guest_write(unsigned int port, unsigned int data)
+{
+    struct domain *currd = current->domain;
+    unsigned long flags;
+
+    switch ( port )
+    {
+    case RTC_PORT(0):
+        /*
+         * All PV domains (and PVH dom0) are allowed to write to the latched
+         * value of the first RTC port, as there's no access to the physical IO
+         * ports.
+         */
+        currd->arch.cmos_idx = data;
+        break;
+
+    case RTC_PORT(1):
+        if ( !ioports_access_permitted(currd, RTC_PORT(0), RTC_PORT(1)) )
+            break;
+        spin_lock_irqsave(&rtc_lock, flags);
+        outb(currd->arch.cmos_idx & 0x7f, RTC_PORT(0));
+        outb(data, RTC_PORT(1));
+        spin_unlock_irqrestore(&rtc_lock, flags);
+        break;
+
+    default:
+        ASSERT_UNREACHABLE();
+    }
+}
+
 static unsigned long get_wallclock_time(void)
 {
 #ifdef CONFIG_XEN_GUEST

xen/include/asm-x86/mc146818rtc.h

@@ -110,4 +110,7 @@ outb_p((val),RTC_PORT(1)); \
 
 #define RTC_IRQ 8
 
+unsigned int rtc_guest_read(unsigned int port);
+void rtc_guest_write(unsigned int port, unsigned int data);
+
 #endif /* _ASM_MC146818RTC_H */