powerpc: Fix regression of per-CPU DSCR setting

Since commit "efcac65 powerpc: Per process DSCR + some fixes (try#4)"
it is no longer possible to set the DSCR on a per-CPU basis.

The old behaviour was to minipulate the DSCR SPR directly but this is no
longer sufficient: the value is quickly overwritten by context switching.

This patch stores the per-CPU DSCR value in a kernel variable rather than
directly in the SPR and it is used whenever a process has not set the DSCR
itself. The sysfs interface (/sys/devices/system/cpu/cpuN/dscr) is unchanged.

Writes to the old global default (/sys/devices/system/cpu/dscr_default)
now set all of the per-CPU values and reads return the last written value.

The new per-CPU default is added to the paca_struct and is used everywhere
outside of sysfs.c instead of the old global default.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 1 insertions, 8 deletions

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 9fde8a1bf1e1..911d45366f59 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -387,12 +387,6 @@ _GLOBAL(ret_from_kernel_thread)
         li      r3,0
         b       syscall_exit
 
-        .section        ".toc","aw"
-DSCR_DEFAULT:
-        .tc dscr_default[TC],dscr_default
-
-        .section        ".text"
-
 /*
  * This routine switches between two different tasks.  The process
  * state of one is saved on its kernel stack.  Then the state
@@ -577,11 +571,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
 #ifdef CONFIG_PPC64
 BEGIN_FTR_SECTION
         lwz     r6,THREAD_DSCR_INHERIT(r4)
-        ld      r7,DSCR_DEFAULT@toc(2)
         ld      r0,THREAD_DSCR(r4)
         cmpwi   r6,0
         bne     1f
-        ld      r0,0(r7)
+        ld      r0,PACA_DSCR(r13)
 1:
 BEGIN_FTR_SECTION_NESTED(70)
         mfspr   r8, SPRN_FSCR