[Xen-changelog] [qemu-upstream-unstable] rtc: Only call rtc_set_cmos when Register B SET flag is disabled.

[patchbot@xxxxxxx]

commit 02c6ccc6dde90dcbf5975b1cfe2ab199e525ec11
Author: Alex Horn <alex.horn@xxxxxxxxxxx>
Date:   Mon Nov 26 17:32:54 2012 +0100

    rtc: Only call rtc_set_cmos when Register B SET flag is disabled.
    
    This bug occurs when the SET flag of Register B is enabled. When an RTC
    data register (i.e. any of the ten time/calender CMOS bytes) is set, the
    data is (as expected) correctly stored in the cmos_data array. However,
    since the SET flag is enabled, the function rtc_set_time is not invoked.
    As a result, the field base_rtc in RTCState remains uninitialized. This
    causes a problem on subsequent writes which can end up overwriting data.
    To see this, consider writing data to Register A after having written
    data to any of the RTC data registers; the following figure illustrates
    the call stack for the Register A write operation:
    
     +- cmos_io_port_write
     +-- check_update_timer
     +---- get_next_alarm
     +------ rtc_update_time
    
    In rtc_update_time, get_guest_rtc calculates the wrong time and
    overwrites the previously written RTC data register values.
    
    Signed-off-by: Alex Horn <alex.horn@xxxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
---
 hw/mc146818rtc.c |    6 +++++-
 tests/rtc-test.c |   40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletions(-)

diff --git a/hw/mc146818rtc.c b/hw/mc146818rtc.c
index 7d84ce3..c79fca7 100644
--- a/hw/mc146818rtc.c
+++ b/hw/mc146818rtc.c
@@ -570,7 +570,11 @@ static void rtc_update_time(RTCState *s)
     guest_nsec = get_guest_rtc_ns(s);
     guest_sec = guest_nsec / NSEC_PER_SEC;
     gmtime_r(&guest_sec, &ret);
-    rtc_set_cmos(s, &ret);
+
+    /* Is SET flag of Register B disabled? */
+    if ((s->cmos_data[RTC_REG_B] & REG_B_SET) == 0) {
+        rtc_set_cmos(s, &ret);
+    }
 }
 
 static int update_in_progress(RTCState *s)
diff --git a/tests/rtc-test.c b/tests/rtc-test.c
index 7fdc94a..02edbf5 100644
--- a/tests/rtc-test.c
+++ b/tests/rtc-test.c
@@ -327,6 +327,45 @@ static void fuzz_registers(void)
     }
 }
 
+static void register_b_set_flag(void)
+{
+    /* Enable binary-coded decimal (BCD) mode and SET flag in Register B*/
+    cmos_write(RTC_REG_B, (cmos_read(RTC_REG_B) & ~REG_B_DM) | REG_B_SET);
+
+    cmos_write(RTC_REG_A, 0x76);
+    cmos_write(RTC_YEAR, 0x11);
+    cmos_write(RTC_CENTURY, 0x20);
+    cmos_write(RTC_MONTH, 0x02);
+    cmos_write(RTC_DAY_OF_MONTH, 0x02);
+    cmos_write(RTC_HOURS, 0x02);
+    cmos_write(RTC_MINUTES, 0x04);
+    cmos_write(RTC_SECONDS, 0x58);
+    cmos_write(RTC_REG_A, 0x26);
+
+    /* Since SET flag is still enabled, these are equality checks. */
+    g_assert_cmpint(cmos_read(RTC_HOURS), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_MINUTES), ==, 0x04);
+    g_assert_cmpint(cmos_read(RTC_SECONDS), ==, 0x58);
+    g_assert_cmpint(cmos_read(RTC_DAY_OF_MONTH), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_MONTH), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_YEAR), ==, 0x11);
+    g_assert_cmpint(cmos_read(RTC_CENTURY), ==, 0x20);
+
+    /* Disable SET flag in Register B */
+    cmos_write(RTC_REG_B, cmos_read(RTC_REG_B) & ~REG_B_SET);
+
+    g_assert_cmpint(cmos_read(RTC_HOURS), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_MINUTES), ==, 0x04);
+
+    /* Since SET flag is disabled, this is an inequality check.
+     * We (reasonably) assume that no (sexagesimal) overflow occurs. */
+    g_assert_cmpint(cmos_read(RTC_SECONDS), >=, 0x58);
+    g_assert_cmpint(cmos_read(RTC_DAY_OF_MONTH), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_MONTH), ==, 0x02);
+    g_assert_cmpint(cmos_read(RTC_YEAR), ==, 0x11);
+    g_assert_cmpint(cmos_read(RTC_CENTURY), ==, 0x20);
+}
+
 int main(int argc, char **argv)
 {
     QTestState *s = NULL;
@@ -342,6 +381,7 @@ int main(int argc, char **argv)
     qtest_add_func("/rtc/alarm-time", alarm_time);
     qtest_add_func("/rtc/set-year/20xx", set_year_20xx);
     qtest_add_func("/rtc/set-year/1980", set_year_1980);
+    qtest_add_func("/rtc/register_b_set_flag", register_b_set_flag);
     qtest_add_func("/rtc/fuzz-registers", fuzz_registers);
     ret = g_test_run();
 
--
generated by git-patchbot for /home/xen/git/qemu-upstream-unstable.git

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog