powerpc: Emulate non privileged DSCR read and write

commit 73d2fb758e678c93bc76d40876c2359f0729b0ef upstream.

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>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
index 51fb00a20d7ea4a02304b43cf14a3a1593ef8350..4f440a65f6e1060e6d8e37a9f7ad492624425da6 100644 (file)
--- a/arch/powerpc/include/asm/ppc-opcode.h
+++ b/arch/powerpc/include/asm/ppc-opcode.h
@@ -112,6 +112,10 @@
 #define PPC_INST_MFSPR_DSCR_MASK       0xfc1fffff
 #define PPC_INST_MTSPR_DSCR            0x7c1103a6
 #define PPC_INST_MTSPR_DSCR_MASK       0xfc1fffff
+#define PPC_INST_MFSPR_DSCR_USER       0x7c0302a6
+#define PPC_INST_MFSPR_DSCR_USER_MASK  0xfc1fffff
+#define PPC_INST_MTSPR_DSCR_USER       0x7c0303a6
+#define PPC_INST_MTSPR_DSCR_USER_MASK  0xfc1fffff
 #define PPC_INST_SLBFEE                        0x7c0007a7
 
 #define PPC_INST_STRING                        0x7c00042a

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 32518401af68d274be52d52cf9249505496d07a9..6686794c963901ead0ab8fe4adf17f9e79f7a92d 100644 (file)
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -961,7 +961,10 @@ 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;
@@ -969,7 +972,10 @@ 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;