arch/tile: support TIF_NOTIFY_RESUME

This support is required for CONFIG_KEYS, NFSv4 kernel DNS, etc.
The change is slightly more complex than the minimal thing, since
I took advantage of having to go into the assembly code to just
move a bunch of stuff into C code: specifically, the schedule(),
do_async_page_fault(), do_signal(), and single_step_once() support,
in addition to the TIF_NOTIFY_RESUME support.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

3 files changed, 73 insertions, 97 deletions

diff --git a/arch/tile/kernel/intvec_32.S b/arch/tile/kernel/intvec_32.S
index fffcfa6b3a62..f35c3124fa62 100644
--- a/arch/tile/kernel/intvec_32.S
+++ b/arch/tile/kernel/intvec_32.S
@@ -851,14 +851,27 @@ STD_ENTRY(interrupt_return)
         /* Check to see if there is any work to do before returning to user. */
         {
          addi   r29, r32, THREAD_INFO_FLAGS_OFFSET
-         moveli r28, lo16(_TIF_ALLWORK_MASK)
+         moveli r1, lo16(_TIF_ALLWORK_MASK)
         }
         {
          lw     r29, r29
-         auli   r28, r28, ha16(_TIF_ALLWORK_MASK)
+         auli   r1, r1, ha16(_TIF_ALLWORK_MASK)
         }
-        and     r28, r29, r28
-        bnz     r28, .Lwork_pending
+        and     r1, r29, r1
+        bzt     r1, .Lrestore_all
+
+        /*
+         * Make sure we have all the registers saved for signal
+         * handling or single-step.  Call out to C code to figure out
+         * exactly what we need to do for each flag bit, then if
+         * necessary, reload the flags and recheck.
+         */
+        push_extra_callee_saves r0
+        {
+         PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
+         jal    do_work_pending
+        }
+        bnz     r0, .Lresume_userspace
 
         /*
          * In the NMI case we
@@ -1099,99 +1112,6 @@ STD_ENTRY(interrupt_return)
         pop_reg r50
         pop_reg r51, sp, PTREGS_OFFSET_REG(29) - PTREGS_OFFSET_REG(51)
         j .Lcontinue_restore_regs
-
-.Lwork_pending:
-        /* Mask the reschedule flag */
-        andi    r28, r29, _TIF_NEED_RESCHED
-
-        {
-         /*
-          * If the NEED_RESCHED flag is called, we call schedule(), which
-          * may drop this context right here and go do something else.
-          * On return, jump back to .Lresume_userspace and recheck.
-          */
-         bz     r28, .Lasync_tlb
-
-         /* Mask the async-tlb flag */
-         andi   r28, r29, _TIF_ASYNC_TLB
-        }
-
-        jal     schedule
-        FEEDBACK_REENTER(interrupt_return)
-
-        /* Reload the flags and check again */
-        j       .Lresume_userspace
-
-.Lasync_tlb:
-        {
-         bz     r28, .Lneed_sigpending
-
-         /* Mask the sigpending flag */
-         andi   r28, r29, _TIF_SIGPENDING
-        }
-
-        PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
-        jal     do_async_page_fault
-        FEEDBACK_REENTER(interrupt_return)
-
-        /*
-         * Go restart the "resume userspace" process.  We may have
-         * fired a signal, and we need to disable interrupts again.
-         */
-        j       .Lresume_userspace
-
-.Lneed_sigpending:
-        /*
-         * At this point we are either doing signal handling or single-step,
-         * so either way make sure we have all the registers saved.
-         */
-        push_extra_callee_saves r0
-
-        {
-         /* If no signal pending, skip to singlestep check */
-         bz     r28, .Lneed_singlestep
-
-         /* Mask the singlestep flag */
-         andi   r28, r29, _TIF_SINGLESTEP
-        }
-
-        jal     do_signal
-        FEEDBACK_REENTER(interrupt_return)
-
-        /* Reload the flags and check again */
-        j       .Lresume_userspace
-
-.Lneed_singlestep:
-        {
-         /* Get a pointer to the EX1 field */
-         PTREGS_PTR(r29, PTREGS_OFFSET_EX1)
-
-         /* If we get here, our bit must be set. */
-         bz     r28, .Lwork_confusion
-        }
-        /* If we are in priv mode, don't single step */
-        lw      r28, r29
-        andi    r28, r28, SPR_EX_CONTEXT_1_1__PL_MASK  /* mask off ICS */
-        bnz     r28, .Lrestore_all
-
-        /* Allow interrupts within the single step code */
-        TRACE_IRQS_ON  /* Note: clobbers registers r0-r29 */
-        IRQ_ENABLE(r20, r21)
-
-        /* try to single-step the current instruction */
-        PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
-        jal     single_step_once
-        FEEDBACK_REENTER(interrupt_return)
-
-        /* Re-disable interrupts.  TRACE_IRQS_OFF in .Lrestore_all. */
-        IRQ_DISABLE(r20,r21)
-
-        j       .Lrestore_all
-
-.Lwork_confusion:
-        move    r0, r28
-        panic   "thread_info allwork flags unhandled on userspace resume: %#x"
-
         STD_ENDPROC(interrupt_return)
 
         /*
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index d0065103eb7b..8e8633490f8b 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -25,10 +25,13 @@
 #include <linux/hardirq.h>
 #include <linux/syscalls.h>
 #include <linux/kernel.h>
+#include <linux/tracehook.h>
+#include <linux/signal.h>
 #include <asm/system.h>
 #include <asm/stack.h>
 #include <asm/homecache.h>
 #include <asm/syscalls.h>
+#include <asm/traps.h>
 #ifdef CONFIG_HARDWALL
 #include <asm/hardwall.h>
 #endif
@@ -546,6 +549,51 @@ struct task_struct *__sched _switch_to(struct task_struct *prev,
         return __switch_to(prev, next, next_current_ksp0(next));
 }
 
+/*
+ * This routine is called on return from interrupt if any of the
+ * TIF_WORK_MASK flags are set in thread_info->flags.  It is
+ * entered with interrupts disabled so we don't miss an event
+ * that modified the thread_info flags.  If any flag is set, we
+ * handle it and return, and the calling assembly code will
+ * re-disable interrupts, reload the thread flags, and call back
+ * if more flags need to be handled.
+ *
+ * We return whether we need to check the thread_info flags again
+ * or not.  Note that we don't clear TIF_SINGLESTEP here, so it's
+ * important that it be tested last, and then claim that we don't
+ * need to recheck the flags.
+ */
+int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
+{
+        if (thread_info_flags & _TIF_NEED_RESCHED) {
+                schedule();
+                return 1;
+        }
+#if CHIP_HAS_TILE_DMA() || CHIP_HAS_SN_PROC()
+        if (thread_info_flags & _TIF_ASYNC_TLB) {
+                do_async_page_fault(regs);
+                return 1;
+        }
+#endif
+        if (thread_info_flags & _TIF_SIGPENDING) {
+                do_signal(regs);
+                return 1;
+        }
+        if (thread_info_flags & _TIF_NOTIFY_RESUME) {
+                clear_thread_flag(TIF_NOTIFY_RESUME);
+                tracehook_notify_resume(regs);
+                if (current->replacement_session_keyring)
+                        key_replace_session_keyring();
+                return 1;
+        }
+        if (thread_info_flags & _TIF_SINGLESTEP) {
+                if ((regs->ex1 & SPR_EX_CONTEXT_1_1__PL_MASK) == 0)
+                        single_step_once(regs);
+                return 0;
+        }
+        panic("work_pending: bad flags %#x\n", thread_info_flags);
+}
+
 /* Note there is an implicit fifth argument if (clone_flags & CLONE_SETTLS). */
 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
                 void __user *, parent_tidptr, void __user *, child_tidptr,
diff --git a/arch/tile/kernel/single_step.c b/arch/tile/kernel/single_step.c
index 84a729e06ec4..86df5a239b70 100644
--- a/arch/tile/kernel/single_step.c
+++ b/arch/tile/kernel/single_step.c
@@ -318,6 +318,14 @@ void single_step_once(struct pt_regs *regs)
 "    .popsection\n"
         );
 
+        /*
+         * Enable interrupts here to allow touching userspace and the like.
+         * The callers expect this: do_trap() already has interrupts
+         * enabled, and do_work_pending() handles functions that enable
+         * interrupts internally.
+         */
+        local_irq_enable();
+
         if (state == NULL) {
                 /* allocate a page of writable, executable memory */
                 state = kmalloc(sizeof(struct single_step_state), GFP_KERNEL);