[PATCH] paravirt: Add option to allow skipping the timer check

Add a way to disable the timer IRQ routing check via a boot option.  The
VMI timer code uses this to avoid triggering the pester Mingo code, which
probes for some very unusual and broken motherboard routings.  It fires
100% of the time when using a paravirtual delay mechanism instead of using
a realtime delay, since there is no elapsed real time, and the 4 timer IRQs
have not yet been delivered.

In addition, it is entirely possible, though improbable, that this bug
could surface on real hardware which picks a particularly bad time to enter
SMM mode, causing a long latency during one of the timer IRQs.

While here, make check_timer be __init.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andi Kleen <ak@suse.de>
[chrisw: use no_timer_check to bring inline with x86_64 as per Andi's request]
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>

2 files changed, 19 insertions, 4 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 2e1898e4e8fd..4e90aa427aea 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -599,8 +599,6 @@ and is between 256 and 4096 characters. It is defined in the file
 
         hugepages=      [HW,IA-32,IA-64] Maximal number of HugeTLB pages.
 
-        noirqbalance    [IA-32,SMP,KNL] Disable kernel irq balancing
-
         i8042.direct    [HW] Put keyboard port into non-translated mode
         i8042.dumbkbd   [HW] Pretend that controller can only read data from
                              keyboard and cannot control its state
@@ -1052,9 +1050,14 @@ and is between 256 and 4096 characters. It is defined in the file
                         in certain environments such as networked servers or
                         real-time systems.
 
+        noirqbalance    [IA-32,SMP,KNL] Disable kernel irq balancing
+
         noirqdebug      [IA-32] Disables the code which attempts to detect and
                         disable unhandled interrupt sources.
 
+        no_timer_check  [IA-32,X86_64,APIC] Disables the code which tests for
+                        broken timer IRQ sources.
+
         noisapnp        [ISAPNP] Disables ISA PnP code.
 
         noinitrd        [RAM] Tells the kernel not to load any configured
diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index e33b7a845299..993150f206ed 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -1932,6 +1932,15 @@ static void __init setup_ioapic_ids_from_mpc(void)
 static void __init setup_ioapic_ids_from_mpc(void) { }
 #endif
 
+static int no_timer_check __initdata;
+
+static int __init notimercheck(char *s)
+{
+        no_timer_check = 1;
+        return 1;
+}
+__setup("no_timer_check", notimercheck);
+
 /*
  * There is a nasty bug in some older SMP boards, their mptable lies
  * about the timer IRQ. We do the following to work around the situation:
@@ -1940,10 +1949,13 @@ static void __init setup_ioapic_ids_from_mpc(void) { }
  *      - if this function detects that timer IRQs are defunct, then we fall
  *        back to ISA timer IRQs
  */
-static int __init timer_irq_works(void)
+int __init timer_irq_works(void)
 {
         unsigned long t1 = jiffies;
 
+        if (no_timer_check)
+                return 1;
+
         local_irq_enable();
         /* Let ten ticks pass... */
         mdelay((10 * 1000) / HZ);
@@ -2214,7 +2226,7 @@ int timer_uses_ioapic_pin_0;
  * is so screwy.  Thanks to Brian Perkins for testing/hacking this beast
  * fanatically on his truly buggy board.
  */
-static inline void check_timer(void)
+static inline void __init check_timer(void)
 {
         int apic1, pin1, apic2, pin2;
         int vector;