powerpc: Ignore reserved field in DCSR and PVR reads and writes

commit 178f3582 upstream.

IBM bit 31 (for the rest of us - bit 0) is a reserved field in the
instruction definition of mtspr and mfspr. Hardware is encouraged to
(and does) ignore it.

As a result, if userspace executes an mtspr DSCR with the reserved bit
set, we get a DSCR facility unavailable exception. The kernel fails to
match against the expected value/mask, and we silently return to
userspace to try and re-execute the same mtspr DSCR instruction. We
loop forever until the process is killed.

We should do something here, and it seems mirroring what hardware does
is the better option vs killing the process. While here, relax the
matching of mfspr PVR too.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[bwh: Backported to 3.2: drop changes to PPC_INST_M{F,T}SPR_DSCR_USER_MASK]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/powerpc/include/asm/ppc-opcode.h

@@ -31,7 +31,7 @@
 #define PPC_INST_MCRXR			0x7c000400
 #define PPC_INST_MCRXR_MASK		0xfc0007fe
 #define PPC_INST_MFSPR_PVR		0x7c1f42a6
-#define PPC_INST_MFSPR_PVR_MASK		0xfc1fffff
+#define PPC_INST_MFSPR_PVR_MASK		0xfc1ffffe
 #define PPC_INST_MSGSND			0x7c00019c
 #define PPC_INST_NOP			0x60000000
 #define PPC_INST_POPCNTB		0x7c0000f4
@@ -42,9 +42,9 @@
 #define PPC_INST_RFDI			0x4c00004e
 #define PPC_INST_RFMCI			0x4c00004c
 #define PPC_INST_MFSPR_DSCR		0x7c1102a6
-#define PPC_INST_MFSPR_DSCR_MASK	0xfc1fffff
+#define PPC_INST_MFSPR_DSCR_MASK	0xfc1ffffe
 #define PPC_INST_MTSPR_DSCR		0x7c1103a6
-#define PPC_INST_MTSPR_DSCR_MASK	0xfc1fffff
+#define PPC_INST_MTSPR_DSCR_MASK	0xfc1ffffe
 
 #define PPC_INST_STRING			0x7c00042a
 #define PPC_INST_STRING_MASK		0xfc0007fe