[MIPS] SMTC: Close tiny holes in the SMTC IPI replay system.

Signed-off-by: Kevin D. Kissell <kevink@paralogos.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

3 files changed, 67 insertions, 17 deletions

diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S
index e29598ae939d..ffa331029e08 100644
--- a/arch/mips/kernel/entry.S
+++ b/arch/mips/kernel/entry.S
@@ -79,11 +79,6 @@ FEXPORT(syscall_exit)
 
 FEXPORT(restore_all)                    # restore full frame
 #ifdef CONFIG_MIPS_MT_SMTC
-/* Detect and execute deferred IPI "interrupts" */
-        LONG_L  s0, TI_REGS($28)
-        LONG_S  sp, TI_REGS($28)
-        jal     deferred_smtc_ipi
-        LONG_S  s0, TI_REGS($28)
 #ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP
 /* Re-arm any temporarily masked interrupts not explicitly "acked" */
         mfc0    v0, CP0_TCSTATUS
@@ -112,6 +107,11 @@ FEXPORT(restore_all)			# restore full frame
         xor     t0, t0, t3
         mtc0    t0, CP0_TCCONTEXT
 #endif /* CONFIG_MIPS_MT_SMTC_IM_BACKSTOP */
+/* Detect and execute deferred IPI "interrupts" */
+        LONG_L  s0, TI_REGS($28)
+        LONG_S  sp, TI_REGS($28)
+        jal     deferred_smtc_ipi
+        LONG_S  s0, TI_REGS($28)
 #endif /* CONFIG_MIPS_MT_SMTC */
         .set    noat
         RESTORE_TEMP
diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
index 05f2708a9029..39b491b9ad87 100644
--- a/arch/mips/kernel/smtc.c
+++ b/arch/mips/kernel/smtc.c
@@ -70,7 +70,7 @@ static atomic_t ipi_timer_latch[NR_CPUS];
 
 #define IPIBUF_PER_CPU 4
 
-static struct smtc_ipi_q IPIQ[NR_CPUS];
+struct smtc_ipi_q IPIQ[NR_CPUS];
 static struct smtc_ipi_q freeIPIq;
 
 
diff --git a/include/asm-mips/stackframe.h b/include/asm-mips/stackframe.h
index 051e1af0bb95..4c37c4e5f72e 100644
--- a/include/asm-mips/stackframe.h
+++ b/include/asm-mips/stackframe.h
@@ -297,14 +297,31 @@
 #ifdef CONFIG_MIPS_MT_SMTC
                 .set    mips32r2
                 /*
-                 * This may not really be necessary if ints are already
-                 * inhibited here.
+                 * We need to make sure the read-modify-write
+                 * of Status below isn't perturbed by an interrupt
+                 * or cross-TC access, so we need to do at least a DMT,
+                 * protected by an interrupt-inhibit. But setting IXMT
+                 * also creates a few-cycle window where an IPI could
+                 * be queued and not be detected before potentially
+                 * returning to a WAIT or user-mode loop. It must be
+                 * replayed.
+                 *
+                 * We're in the middle of a context switch, and
+                 * we can't dispatch it directly without trashing
+                 * some registers, so we'll try to detect this unlikely
+                 * case and program a software interrupt in the VPE,
+                 * as would be done for a cross-VPE IPI.  To accomodate
+                 * the handling of that case, we're doing a DVPE instead
+                 * of just a DMT here to protect against other threads.
+                 * This is a lot of cruft to cover a tiny window.
+                 * If you can find a better design, implement it!
+                 *
                  */
                 mfc0    v0, CP0_TCSTATUS
                 ori     v0, TCSTATUS_IXMT
                 mtc0    v0, CP0_TCSTATUS
                 _ehb
-                DMT     5                               # dmt a1
+                DVPE    5                               # dvpe a1
                 jal     mips_ihb
 #endif /* CONFIG_MIPS_MT_SMTC */
                 mfc0    a0, CP0_STATUS
@@ -325,17 +342,50 @@
  */
                 LONG_L  v1, PT_TCSTATUS(sp)
                 _ehb
-                mfc0    v0, CP0_TCSTATUS
+                mfc0    a0, CP0_TCSTATUS
                 andi    v1, TCSTATUS_IXMT
-                /* We know that TCStatua.IXMT should be set from above */
-                xori    v0, v0, TCSTATUS_IXMT
-                or      v0, v0, v1
-                mtc0    v0, CP0_TCSTATUS
-                _ehb
-                andi    a1, a1, VPECONTROL_TE
+                bnez    v1, 0f
+
+/*
+ * We'd like to detect any IPIs queued in the tiny window
+ * above and request an software interrupt to service them
+ * when we ERET.
+ *
+ * Computing the offset into the IPIQ array of the executing
+ * TC's IPI queue in-line would be tedious.  We use part of
+ * the TCContext register to hold 16 bits of offset that we
+ * can add in-line to find the queue head.
+ */
+                mfc0    v0, CP0_TCCONTEXT
+                la      a2, IPIQ
+                srl     v0, v0, 16
+                addu    a2, a2, v0
+                LONG_L  v0, 0(a2)
+                beqz    v0, 0f
+/*
+ * If we have a queue, provoke dispatch within the VPE by setting C_SW1
+ */
+                mfc0    v0, CP0_CAUSE
+                ori     v0, v0, C_SW1
+                mtc0    v0, CP0_CAUSE
+0:
+                /*
+                 * This test should really never branch but
+                 * let's be prudent here.  Having atomized
+                 * the shared register modifications, we can
+                 * now EVPE, and must do so before interrupts
+                 * are potentially re-enabled.
+                 */
+                andi    a1, a1, MVPCONTROL_EVP
                 beqz    a1, 1f
-                emt
+                evpe
 1:
+                /* We know that TCStatua.IXMT should be set from above */
+                xori    a0, a0, TCSTATUS_IXMT
+                or      a0, a0, v1
+                mtc0    a0, CP0_TCSTATUS
+                _ehb
+
                 .set    mips0
 #endif /* CONFIG_MIPS_MT_SMTC */
                 LONG_L  v1, PT_EPC(sp)