[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>

1 files changed, 5 insertions, 2 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