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Subject[PATCH v2 15/18] powerpc: Emulate paste instruction
Date
From: Michael Neuling <mikey@neuling.org>

On POWER9 DD2.1 and below there are issues when the paste instruction
generates an error. If an error occurs when thread reconfiguration
happens (ie another thread in the core goes into/out of powersave) the
core may hang.

To avoid this a special sequence is required which stops thread
configuration so that the paste can be safely executed.

This patch assumes paste executed in userspace are trapped into the
illegal instruction exception at 0xe40.

Here we re-execute the paste instruction but with the required
sequence to ensure thread reconfiguration doesn't occur.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---

Edit by Sukadev: Use PPC_PASTE() rather than the paste instruction since
in older versions the instruction required a third parameter.
---
arch/powerpc/include/asm/emulated_ops.h | 1 +
arch/powerpc/include/asm/ppc-opcode.h | 1 +
arch/powerpc/include/asm/reg.h | 2 ++
arch/powerpc/kernel/traps.c | 64 +++++++++++++++++++++++++++++++++
4 files changed, 68 insertions(+)

diff --git a/arch/powerpc/include/asm/emulated_ops.h b/arch/powerpc/include/asm/emulated_ops.h
index f00e10e..9247af9 100644
--- a/arch/powerpc/include/asm/emulated_ops.h
+++ b/arch/powerpc/include/asm/emulated_ops.h
@@ -55,6 +55,7 @@ extern struct ppc_emulated {
struct ppc_emulated_entry mfdscr;
struct ppc_emulated_entry mtdscr;
struct ppc_emulated_entry lq_stq;
+ struct ppc_emulated_entry paste;
#endif
} ppc_emulated;

diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
index ce0930d..a55d2ef 100644
--- a/arch/powerpc/include/asm/ppc-opcode.h
+++ b/arch/powerpc/include/asm/ppc-opcode.h
@@ -229,6 +229,7 @@
#define PPC_INST_MTTMR 0x7c0003dc
#define PPC_INST_NOP 0x60000000
#define PPC_INST_PASTE 0x7c20070d
+#define PPC_INST_PASTE_MASK 0xfc2007ff
#define PPC_INST_POPCNTB 0x7c0000f4
#define PPC_INST_POPCNTB_MASK 0xfc0007fe
#define PPC_INST_POPCNTD 0x7c0003f4
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index f92eaf7..5cde1c4 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -468,6 +468,8 @@
#define SPRN_DBAT7U 0x23E /* Data BAT 7 Upper Register */
#define SPRN_PPR 0x380 /* SMT Thread status Register */
#define SPRN_TSCR 0x399 /* Thread Switch Control Register */
+#define SPRN_TRIG1 0x371 /* WAT Trigger 1 */
+#define SPRN_TRIG2 0x372 /* WAT Trigger 2 */

#define SPRN_DEC 0x016 /* Decrement Register */
#define SPRN_DER 0x095 /* Debug Enable Register */
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 13c9dcd..7e6b1fe 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -956,6 +956,65 @@ static inline bool tm_abort_check(struct pt_regs *regs, int reason)
}
#endif

+static DEFINE_SPINLOCK(paste_emulation_lock);
+
+static inline int paste(void *i)
+{
+ int cr;
+ long retval = 0;
+
+ /* Need per core lock to ensure trig1/2 writes don't race */
+ spin_lock(&paste_emulation_lock);
+ mtspr(SPRN_TRIG1, 0); /* data doesn't matter */
+ mtspr(SPRN_TRIG1, 0); /* HW says do this twice */
+ asm volatile(
+ "1: " PPC_PASTE(0, %2) "\n"
+ "2: mfcr %1\n"
+ ".section .fixup,\"ax\"\n"
+ "3: li %0,%3\n"
+ " li %2,0\n"
+ " b 2b\n"
+ ".previous\n"
+ EX_TABLE(1b, 3b)
+ : "=r" (retval), "=r" (cr)
+ : "b" (i), "i" (-EFAULT), "0" (retval));
+ mtspr(SPRN_TRIG2, 0);
+ spin_unlock(&paste_emulation_lock);
+ return cr;
+}
+
+static int emulate_paste(struct pt_regs *regs, u32 instword)
+{
+ const void __user *addr;
+ unsigned long ea;
+ u8 ra, rb;
+
+ if (!cpu_has_feature(CPU_FTR_ARCH_300))
+ return -EINVAL;
+
+ ra = (instword >> 16) & 0x1f;
+ rb = (instword >> 11) & 0x1f;
+
+ ea = regs->gpr[rb] + (ra ? regs->gpr[ra] : 0ul);
+ if (is_32bit_task())
+ ea &= 0xfffffffful;
+ addr = (__force const void __user *)ea;
+
+ if (!access_ok(VERIFY_WRITE, addr, 128)) // cacheline size == 128
+ return -EFAULT;
+
+ hard_irq_disable(); /* FIXME: could we just soft disable ?? */
+ pagefault_disable();
+
+ PPC_WARN_EMULATED(paste, regs);
+ regs->ccr = paste((void *)addr);
+
+ pagefault_enable();
+ may_hard_irq_enable();
+
+ return 0;
+}
+
static int emulate_instruction(struct pt_regs *regs)
{
u32 instword;
@@ -968,6 +1027,10 @@ static int emulate_instruction(struct pt_regs *regs)
if (get_user(instword, (u32 __user *)(regs->nip)))
return -EFAULT;

+ /* Emulate the paste RA, RB. */
+ if ((instword & PPC_INST_PASTE_MASK) == PPC_INST_PASTE)
+ return emulate_paste(regs, instword);
+
/* Emulate the mfspr rD, PVR. */
if ((instword & PPC_INST_MFSPR_PVR_MASK) == PPC_INST_MFSPR_PVR) {
PPC_WARN_EMULATED(mfpvr, regs);
@@ -1924,6 +1987,7 @@ struct ppc_emulated ppc_emulated = {
WARN_EMULATED_SETUP(mfdscr),
WARN_EMULATED_SETUP(mtdscr),
WARN_EMULATED_SETUP(lq_stq),
+ WARN_EMULATED_SETUP(paste),
#endif
};

--
2.7.4
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