powerpc: Per process DSCR + some fixes (try#4)

The DSCR (aka Data Stream Control Register) is supported on some
server PowerPC chips and allow some control over the prefetch
of data streams.

This patch allows the value to be specified per thread by emulating
the corresponding mfspr and mtspr instructions. Children of such
threads inherit the value. Other threads use a default value that
can be specified in sysfs - /sys/devices/system/cpu/dscr_default.

If a thread starts with non default value in the sysfs entry,
all children threads inherit this non default value even if
the sysfs value is changed later.

Signed-off-by: Alexey Kardashevskiy <aik@au1.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 5ddb801bc154..cb71cf29edea 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -909,6 +909,26 @@ static int emulate_instruction(struct pt_regs *regs)
                 return emulate_isel(regs, instword);
         }
 
+#ifdef CONFIG_PPC64
+        /* Emulate the mfspr rD, DSCR. */
+        if (((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;
+                regs->gpr[rd] = mfspr(SPRN_DSCR);
+                return 0;
+        }
+        /* Emulate the mtspr DSCR, rD. */
+        if (((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;
+                mtspr(SPRN_DSCR, regs->gpr[rd]);
+                current->thread.dscr_inherit = 1;
+                return 0;
+        }
+#endif
+
         return -EINVAL;
 }
 
@@ -1506,6 +1526,10 @@ struct ppc_emulated ppc_emulated = {
 #ifdef CONFIG_VSX
         WARN_EMULATED_SETUP(vsx),
 #endif
+#ifdef CONFIG_PPC64
+        WARN_EMULATED_SETUP(mfdscr),
+        WARN_EMULATED_SETUP(mtdscr),
+#endif
 };
 
 u32 ppc_warn_emulated;