tile: support GENERIC_KERNEL_THREAD and GENERIC_KERNEL_EXECVE

Also provide an optimized current_pt_regs() while we're at it.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

4 files changed, 69 insertions, 75 deletions

diff --git a/arch/tile/kernel/entry.S b/arch/tile/kernel/entry.S
index c31637baff28..f116cb0bce20 100644
--- a/arch/tile/kernel/entry.S
+++ b/arch/tile/kernel/entry.S
@@ -28,17 +28,6 @@ STD_ENTRY(current_text_addr)
         STD_ENDPROC(current_text_addr)
 
 /*
- * Implement execve().  The i386 code has a note that forking from kernel
- * space results in no copy on write until the execve, so we should be
- * careful not to write to the stack here.
- */
-STD_ENTRY(kernel_execve)
-        moveli TREG_SYSCALL_NR_NAME, __NR_execve
-        swint1
-        jrp lr
-        STD_ENDPROC(kernel_execve)
-
-/*
  * We don't run this function directly, but instead copy it to a page
  * we map into every user process.  See vdso_setup().
  *
diff --git a/arch/tile/kernel/intvec_32.S b/arch/tile/kernel/intvec_32.S
index 6943515100f8..58aad519b7d6 100644
--- a/arch/tile/kernel/intvec_32.S
+++ b/arch/tile/kernel/intvec_32.S
@@ -1291,6 +1291,21 @@ STD_ENTRY(ret_from_fork)
         }
         STD_ENDPROC(ret_from_fork)
 
+STD_ENTRY(ret_from_kernel_thread)
+        jal     sim_notify_fork
+        jal     schedule_tail
+        FEEDBACK_REENTER(ret_from_fork)
+        {
+         move   r0, r31
+         jalr   r30
+        }
+        FEEDBACK_REENTER(ret_from_kernel_thread)
+        {
+         movei  r30, 0               /* not an NMI */
+         j      .Lresume_userspace   /* jump into middle of interrupt_return */
+        }
+        STD_ENDPROC(ret_from_kernel_thread)
+
         /*
          * Code for ill interrupt.
          */
diff --git a/arch/tile/kernel/intvec_64.S b/arch/tile/kernel/intvec_64.S
index 73f6c0a648c4..f66bd5f67d44 100644
--- a/arch/tile/kernel/intvec_64.S
+++ b/arch/tile/kernel/intvec_64.S
@@ -1150,6 +1150,21 @@ STD_ENTRY(ret_from_fork)
         }
         STD_ENDPROC(ret_from_fork)
 
+STD_ENTRY(ret_from_kernel_thread)
+        jal     sim_notify_fork
+        jal     schedule_tail
+        FEEDBACK_REENTER(ret_from_fork)
+        {
+         move   r0, r31
+         jalr   r30
+        }
+        FEEDBACK_REENTER(ret_from_kernel_thread)
+        {
+         movei  r30, 0               /* not an NMI */
+         j      .Lresume_userspace   /* jump into middle of interrupt_return */
+        }
+        STD_ENDPROC(ret_from_kernel_thread)
+
 /* Various stub interrupt handlers and syscall handlers */
 
 STD_ENTRY_LOCAL(_kernel_double_fault)
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 9dc139127f86..da6e4d78da6e 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -157,24 +157,44 @@ void arch_release_thread_info(struct thread_info *info)
 static void save_arch_state(struct thread_struct *t);
 
 int copy_thread(unsigned long clone_flags, unsigned long sp,
-                unsigned long stack_size,
+                unsigned long arg,
                 struct task_struct *p, struct pt_regs *regs)
 {
-        struct pt_regs *childregs;
+        struct pt_regs *childregs = task_pt_regs(p);
         unsigned long ksp;
+        unsigned long *callee_regs;
 
         /*
-         * When creating a new kernel thread we pass sp as zero.
-         * Assign it to a reasonable value now that we have the stack.
+         * Set up the stack and stack pointer appropriately for the
+         * new child to find itself woken up in __switch_to().
+         * The callee-saved registers must be on the stack to be read;
+         * the new task will then jump to assembly support to handle
+         * calling schedule_tail(), etc., and (for userspace tasks)
+         * returning to the context set up in the pt_regs.
          */
-        if (sp == 0 && regs->ex1 == PL_ICS_EX1(KERNEL_PL, 0))
-                sp = KSTK_TOP(p);
+        ksp = (unsigned long) childregs;
+        ksp -= C_ABI_SAVE_AREA_SIZE;   /* interrupt-entry save area */
+        ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
+        ksp -= CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long);
+        callee_regs = (unsigned long *)ksp;
+        ksp -= C_ABI_SAVE_AREA_SIZE;   /* __switch_to() save area */
+        ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
+        p->thread.ksp = ksp;
 
-        /*
-         * Do not clone step state from the parent; each thread
-         * must make its own lazily.
-         */
-        task_thread_info(p)->step_state = NULL;
+        /* Record the pid of the task that created this one. */
+        p->thread.creator_pid = current->pid;
+
+        if (unlikely(!regs)) {
+                /* kernel thread */
+                memset(childregs, 0, sizeof(struct pt_regs));
+                memset(&callee_regs[2], 0,
+                       (CALLEE_SAVED_REGS_COUNT - 2) * sizeof(unsigned long));
+                callee_regs[0] = sp;   /* r30 = function */
+                callee_regs[1] = arg;  /* r31 = arg */
+                childregs->ex1 = PL_ICS_EX1(KERNEL_PL, 0);
+                p->thread.pc = (unsigned long) ret_from_kernel_thread;
+                return 0;
+        }
 
         /*
          * Start new thread in ret_from_fork so it schedules properly
@@ -182,20 +202,24 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
          */
         p->thread.pc = (unsigned long) ret_from_fork;
 
+        /*
+         * Do not clone step state from the parent; each thread
+         * must make its own lazily.
+         */
+        task_thread_info(p)->step_state = NULL;
+
         /* Save user stack top pointer so we can ID the stack vm area later. */
         p->thread.usp0 = sp;
 
-        /* Record the pid of the process that created this one. */
-        p->thread.creator_pid = current->pid;
-
         /*
          * Copy the registers onto the kernel stack so the
          * return-from-interrupt code will reload it into registers.
          */
-        childregs = task_pt_regs(p);
         *childregs = *regs;
         childregs->regs[0] = 0;         /* return value is zero */
         childregs->sp = sp;  /* override with new user stack pointer */
+        memcpy(callee_regs, &regs->regs[CALLEE_SAVED_FIRST_REG],
+               CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long));
 
         /*
          * If CLONE_SETTLS is set, set "tp" in the new task to "r4",
@@ -204,24 +228,6 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
         if (clone_flags & CLONE_SETTLS)
                 childregs->tp = regs->regs[4];
 
-        /*
-         * Copy the callee-saved registers from the passed pt_regs struct
-         * into the context-switch callee-saved registers area.
-         * This way when we start the interrupt-return sequence, the
-         * callee-save registers will be correctly in registers, which
-         * is how we assume the compiler leaves them as we start doing
-         * the normal return-from-interrupt path after calling C code.
-         * Zero out the C ABI save area to mark the top of the stack.
-         */
-        ksp = (unsigned long) childregs;
-        ksp -= C_ABI_SAVE_AREA_SIZE;   /* interrupt-entry save area */
-        ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
-        ksp -= CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long);
-        memcpy((void *)ksp, &regs->regs[CALLEE_SAVED_FIRST_REG],
-               CALLEE_SAVED_REGS_COUNT * sizeof(unsigned long));
-        ksp -= C_ABI_SAVE_AREA_SIZE;   /* __switch_to() save area */
-        ((long *)ksp)[0] = ((long *)ksp)[1] = 0;
-        p->thread.ksp = ksp;
 
 #if CHIP_HAS_TILE_DMA()
         /*
@@ -650,37 +656,6 @@ unsigned long get_wchan(struct task_struct *p)
         return 0;
 }
 
-/*
- * We pass in lr as zero (cleared in kernel_thread) and the caller
- * part of the backtrace ABI on the stack also zeroed (in copy_thread)
- * so that backtraces will stop with this function.
- * Note that we don't use r0, since copy_thread() clears it.
- */
-static void start_kernel_thread(int dummy, int (*fn)(int), int arg)
-{
-        do_exit(fn(arg));
-}
-
-/*
- * Create a kernel thread
- */
-int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
-{
-        struct pt_regs regs;
-
-        memset(&regs, 0, sizeof(regs));
-        regs.ex1 = PL_ICS_EX1(KERNEL_PL, 0);  /* run at kernel PL, no ICS */
-        regs.pc = (long) start_kernel_thread;
-        regs.flags = PT_FLAGS_CALLER_SAVES;   /* need to restore r1 and r2 */
-        regs.regs[1] = (long) fn;             /* function pointer */
-        regs.regs[2] = (long) arg;            /* parameter register */
-
-        /* Ok, create the new process.. */
-        return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs,
-                       0, NULL, NULL);
-}
-EXPORT_SYMBOL(kernel_thread);
-
 /* Flush thread state. */
 void flush_thread(void)
 {