[PATCH] x86-64: update IO-APIC dest field to 8-bit for xAPIC

On the Unisys ES7000/ONE system, we encountered a problem where performing
a kexec reboot or dump on any cell other than cell 0 causes the system
timer to stop working, resulting in a hang during timer calibration in the
new kernel.

We traced the problem to one line of code in disable_IO_APIC(), which needs
to restore the timer's IO-APIC configuration before rebooting.  The code is
currently using the 4-bit physical destination field, rather than using the
8-bit logical destination field, and it cuts off the upper 4 bits of the
timer's APIC ID.  If we change this to use the logical destination field,
the timer works and we can kexec on the upper cells.  This was tested on
two different cells (0 and 2) in an ES7000/ONE system.

For reference, the relevant Intel xAPIC spec is kept at
ftp://download.intel.com/design/chipsets/e8501/datashts/30962001.pdf,
specifically on page 334.

Signed-off-by: Benjamin M Romer <benjamin.romer@unisys.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 12 deletions

diff --git a/include/asm-x86_64/io_apic.h b/include/asm-x86_64/io_apic.h
index 561ecbfd4cb5..f4fb238c89f1 100644
--- a/include/asm-x86_64/io_apic.h
+++ b/include/asm-x86_64/io_apic.h
@@ -85,18 +85,8 @@ struct IO_APIC_route_entry {
                 mask            :  1,   /* 0: enabled, 1: disabled */
                 __reserved_2    : 15;
 
-        union {         struct { __u32
-                                        __reserved_1    : 24,
-                                        physical_dest   :  4,
-                                        __reserved_2    :  4;
-                        } physical;
-
-                        struct { __u32
-                                        __reserved_1    : 24,
-                                        logical_dest    :  8;
-                        } logical;
-        } dest;
-
+        __u32   __reserved_3    : 24,
+                dest            :  8;
 } __attribute__ ((packed));
 
 /*