powerpc: Emulate non privileged DSCR read and write

POWER8 allows read and write of the DSCR in userspace. We added
kernel emulation so applications could always use the instructions
regardless of the CPU type.

Unfortunately there are two SPRs for the DSCR and we only added
emulation for the privileged one. Add code to match the non
privileged one.

A simple test was created to verify the fix:

http://ozlabs.org/~anton/junkcode/user_dscr_test.c

Without the patch we get a SIGILL and it passes with the patch.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: <stable@kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 37cc40ef5043..83efa2f7d926 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -970,7 +970,10 @@ static int emulate_instruction(struct pt_regs *regs)
 
 #ifdef CONFIG_PPC64
         /* Emulate the mfspr rD, DSCR. */
-        if (((instword & PPC_INST_MFSPR_DSCR_MASK) == PPC_INST_MFSPR_DSCR) &&
+        if ((((instword & PPC_INST_MFSPR_DSCR_USER_MASK) ==
+                PPC_INST_MFSPR_DSCR_USER) ||
+             ((instword & PPC_INST_MFSPR_DSCR_MASK) ==
+                PPC_INST_MFSPR_DSCR)) &&
                         cpu_has_feature(CPU_FTR_DSCR)) {
                 PPC_WARN_EMULATED(mfdscr, regs);
                 rd = (instword >> 21) & 0x1f;
@@ -978,7 +981,10 @@ static int emulate_instruction(struct pt_regs *regs)
                 return 0;
         }
         /* Emulate the mtspr DSCR, rD. */
-        if (((instword & PPC_INST_MTSPR_DSCR_MASK) == PPC_INST_MTSPR_DSCR) &&
+        if ((((instword & PPC_INST_MTSPR_DSCR_USER_MASK) ==
+                PPC_INST_MTSPR_DSCR_USER) ||
+             ((instword & PPC_INST_MTSPR_DSCR_MASK) ==
+                PPC_INST_MTSPR_DSCR)) &&
                         cpu_has_feature(CPU_FTR_DSCR)) {
                 PPC_WARN_EMULATED(mtdscr, regs);
                 rd = (instword >> 21) & 0x1f;