src/patches/suse-2.6.27.31/patches.arch/ppc-syscall-xer.so.1.patch

   1 Subject: Fix system calls on Cell entered with XER.SO=1
   2 From: Paul Mackerras <paulus@samba.org>
   3 References: 456406 - LTC50395
   4
   5
   6 It turns out that on Cell, on a kernel with CONFIG_VIRT_CPU_ACCOUNTING=y,
   7 if a program sets the SO (summary overflow) bit in the XER and
   8 then does a system call, the SO bit in CR0 will be set on return
   9 regardless of whether the system call detected an error.  Since CR0.SO
  10 is used as the error indication from the system call, this means that
  11 all system calls appear to fail.
  12
  13 The reason is that the workaround for the timebase bug on Cell uses a
  14 compare instruction.  With CONFIG_VIRT_CPU_ACCOUNTING = y, the
  15 ACCOUNT_CPU_USER_ENTRY macro reads the timebase, so we end up doing a
  16 compare instruction, which copies XER.SO to CR0.SO.  Since we were
  17 doing this in the system call entry patch after clearing CR0.SO but
  18 before saving the CR, this meant that the saved CR image had CR0.SO
  19 set if XER.SO was set on entry.
  20
  21 This fixes it by moving the clearing of CR0.SO to after the
  22 ACCOUNT_CPU_USER_ENTRY call in the system call entry path.
  23
  24 Signed-off-by: Paul Mackerras <paulus@samba.org>
  25 Acked-by: Arnd Bergmann <arnd@arndb.de>
  26 Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
  27 Signed-off-by: Olaf Hering <olh@suse.de>
  28
  29 ---
  30  arch/powerpc/kernel/entry_64.S |    2 +-
  31  1 file changed, 1 insertion(+), 1 deletion(-)
  32
  33 --- a/arch/powerpc/kernel/entry_64.S
  34 +++ b/arch/powerpc/kernel/entry_64.S
  35 @@ -57,12 +57,12 @@ system_call_common:
  36         beq-    1f
  37         ld      r1,PACAKSAVE(r13)
  38  1:     std     r10,0(r1)
  39 -       crclr   so
  40         std     r11,_NIP(r1)
  41         std     r12,_MSR(r1)
  42         std     r0,GPR0(r1)
  43         std     r10,GPR1(r1)
  44         ACCOUNT_CPU_USER_ENTRY(r10, r11)
  45 +       crclr   so
  46         std     r2,GPR2(r1)
  47         std     r3,GPR3(r1)
  48         std     r4,GPR4(r1)