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+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * wuf.S: Window underflow trap handler for the Sparc.
+ *
+ * Copyright (C) 1995 David S. Miller
+ */
+
+#include <asm/contregs.h>
+#include <asm/page.h>
+#include <asm/ptrace.h>
+#include <asm/psr.h>
+#include <asm/smp.h>
+#include <asm/asi.h>
+#include <asm/winmacro.h>
+#include <asm/asmmacro.h>
+#include <asm/thread_info.h>
+
+/* Just like the overflow handler we define macros for registers
+ * with fixed meanings in this routine.
+ */
+#define t_psr l0
+#define t_pc l1
+#define t_npc l2
+#define t_wim l3
+/* Don't touch the above registers or else you die horribly... */
+
+/* Now macros for the available scratch registers in this routine. */
+#define twin_tmp1 l4
+#define twin_tmp2 l5
+
+#define curptr g6
+
+ .text
+ .align 4
+
+ /* The trap entry point has executed the following:
+ *
+ * rd %psr, %l0
+ * rd %wim, %l3
+ * b fill_window_entry
+ * andcc %l0, PSR_PS, %g0
+ */
+
+ /* Datum current_thread_info->uwinmask contains at all times a bitmask
+ * where if any user windows are active, at least one bit will
+ * be set in to mask. If no user windows are active, the bitmask
+ * will be all zeroes.
+ */
+
+ /* To get an idea of what has just happened to cause this
+ * trap take a look at this diagram:
+ *
+ * 1 2 3 4 <-- Window number
+ * ----------
+ * T O W I <-- Symbolic name
+ *
+ * O == the window that execution was in when
+ * the restore was attempted
+ *
+ * T == the trap itself has save'd us into this
+ * window
+ *
+ * W == this window is the one which is now invalid
+ * and must be made valid plus loaded from the
+ * stack
+ *
+ * I == this window will be the invalid one when we
+ * are done and return from trap if successful
+ */
+
+ /* BEGINNING OF PATCH INSTRUCTIONS */
+
+ /* On 7-window Sparc the boot code patches fnwin_patch1
+ * with the following instruction.
+ */
+ .globl fnwin_patch1_7win, fnwin_patch2_7win
+fnwin_patch1_7win: srl %t_wim, 6, %twin_tmp2
+fnwin_patch2_7win: and %twin_tmp1, 0x7f, %twin_tmp1
+ /* END OF PATCH INSTRUCTIONS */
+
+ .globl fill_window_entry, fnwin_patch1, fnwin_patch2
+fill_window_entry:
+ /* LOCATION: Window 'T' */
+
+ /* Compute what the new %wim is going to be if we retrieve
+ * the proper window off of the stack.
+ */
+ sll %t_wim, 1, %twin_tmp1
+fnwin_patch1: srl %t_wim, 7, %twin_tmp2
+ or %twin_tmp1, %twin_tmp2, %twin_tmp1
+fnwin_patch2: and %twin_tmp1, 0xff, %twin_tmp1
+
+ wr %twin_tmp1, 0x0, %wim /* Make window 'I' invalid */
+
+ andcc %t_psr, PSR_PS, %g0
+ be fwin_from_user
+ restore %g0, %g0, %g0 /* Restore to window 'O' */
+
+ /* Trapped from kernel, we trust that the kernel does not
+ * 'over restore' sorta speak and just grab the window
+ * from the stack and return. Easy enough.
+ */
+fwin_from_kernel:
+ /* LOCATION: Window 'O' */
+
+ restore %g0, %g0, %g0
+
+ /* LOCATION: Window 'W' */
+
+ LOAD_WINDOW(sp) /* Load it up */
+
+ /* Spin the wheel... */
+ save %g0, %g0, %g0
+ save %g0, %g0, %g0
+ /* I'd like to buy a vowel please... */
+
+ /* LOCATION: Window 'T' */
+
+ /* Now preserve the condition codes in %psr, pause, and
+ * return from trap. This is the simplest case of all.
+ */
+ wr %t_psr, 0x0, %psr
+ WRITE_PAUSE
+
+ jmp %t_pc
+ rett %t_npc
+
+fwin_from_user:
+ /* LOCATION: Window 'O' */
+
+ restore %g0, %g0, %g0 /* Restore to window 'W' */
+
+ /* LOCATION: Window 'W' */
+
+ /* Branch to the stack validation routine */
+ b srmmu_fwin_stackchk
+ andcc %sp, 0x7, %g0
+
+#define STACK_OFFSET (THREAD_SIZE - TRACEREG_SZ - STACKFRAME_SZ)
+
+fwin_user_stack_is_bolixed:
+ /* LOCATION: Window 'W' */
+
+ /* Place a pt_regs frame on the kernel stack, save back
+ * to the trap window and call c-code to deal with this.
+ */
+ LOAD_CURRENT(l4, l5)
+
+ sethi %hi(STACK_OFFSET), %l5
+ or %l5, %lo(STACK_OFFSET), %l5
+ add %l4, %l5, %l5
+
+ /* Store globals into pt_regs frame. */
+ STORE_PT_GLOBALS(l5)
+ STORE_PT_YREG(l5, g3)
+
+ /* Save current in a global while we change windows. */
+ mov %l4, %curptr
+
+ save %g0, %g0, %g0
+
+ /* LOCATION: Window 'O' */
+
+ rd %psr, %g3 /* Read %psr in live user window */
+ mov %fp, %g4 /* Save bogus frame pointer. */
+
+ save %g0, %g0, %g0
+
+ /* LOCATION: Window 'T' */
+
+ sethi %hi(STACK_OFFSET), %l5
+ or %l5, %lo(STACK_OFFSET), %l5
+ add %curptr, %l5, %sp
+
+ /* Build rest of pt_regs. */
+ STORE_PT_INS(sp)
+ STORE_PT_PRIV(sp, t_psr, t_pc, t_npc)
+
+ /* re-set trap time %wim value */
+ wr %t_wim, 0x0, %wim
+
+ /* Fix users window mask and buffer save count. */
+ mov 0x1, %g5
+ sll %g5, %g3, %g5
+ st %g5, [%curptr + TI_UWINMASK] ! one live user window still
+ st %g0, [%curptr + TI_W_SAVED] ! no windows in the buffer
+
+ wr %t_psr, PSR_ET, %psr ! enable traps
+ nop
+ call window_underflow_fault
+ mov %g4, %o0
+
+ b ret_trap_entry
+ clr %l6
+
+fwin_user_stack_is_ok:
+ /* LOCATION: Window 'W' */
+
+ /* The users stack area is kosher and mapped, load the
+ * window and fall through to the finish up routine.
+ */
+ LOAD_WINDOW(sp)
+
+ /* Round and round she goes... */
+ save %g0, %g0, %g0 /* Save to window 'O' */
+ save %g0, %g0, %g0 /* Save to window 'T' */
+ /* Where she'll trap nobody knows... */
+
+ /* LOCATION: Window 'T' */
+
+fwin_user_finish_up:
+ /* LOCATION: Window 'T' */
+
+ wr %t_psr, 0x0, %psr
+ WRITE_PAUSE
+
+ jmp %t_pc
+ rett %t_npc
+
+ /* Here come the architecture specific checks for stack.
+ * mappings. Note that unlike the window overflow handler
+ * we only need to check whether the user can read from
+ * the appropriate addresses. Also note that we are in
+ * an invalid window which will be loaded, and this means
+ * that until we actually load the window up we are free
+ * to use any of the local registers contained within.
+ *
+ * On success these routine branch to fwin_user_stack_is_ok
+ * if the area at %sp is user readable and the window still
+ * needs to be loaded, else fwin_user_finish_up if the
+ * routine has done the loading itself. On failure (bogus
+ * user stack) the routine shall branch to the label called
+ * fwin_user_stack_is_bolixed.
+ *
+ * Contrary to the arch-specific window overflow stack
+ * check routines in wof.S, these routines are free to use
+ * any of the local registers they want to as this window
+ * does not belong to anyone at this point, however the
+ * outs and ins are still verboten as they are part of
+ * 'someone elses' window possibly.
+ */
+
+ .globl srmmu_fwin_stackchk
+srmmu_fwin_stackchk:
+ /* LOCATION: Window 'W' */
+
+ /* Caller did 'andcc %sp, 0x7, %g0' */
+ bne fwin_user_stack_is_bolixed
+ sethi %hi(PAGE_OFFSET), %l5
+
+ /* Check if the users stack is in kernel vma, then our
+ * trial and error technique below would succeed for
+ * the 'wrong' reason.
+ */
+ mov AC_M_SFSR, %l4
+ cmp %l5, %sp
+ bleu fwin_user_stack_is_bolixed
+LEON_PI( lda [%l4] ASI_LEON_MMUREGS, %g0) ! clear fault status
+SUN_PI_( lda [%l4] ASI_M_MMUREGS, %g0) ! clear fault status
+
+ /* The technique is, turn off faults on this processor,
+ * just let the load rip, then check the sfsr to see if
+ * a fault did occur. Then we turn on fault traps again
+ * and branch conditionally based upon what happened.
+ */
+LEON_PI(lda [%g0] ASI_LEON_MMUREGS, %l5) ! read mmu-ctrl reg
+SUN_PI_(lda [%g0] ASI_M_MMUREGS, %l5) ! read mmu-ctrl reg
+ or %l5, 0x2, %l5 ! turn on no-fault bit
+LEON_PI(sta %l5, [%g0] ASI_LEON_MMUREGS) ! store it
+SUN_PI_(sta %l5, [%g0] ASI_M_MMUREGS) ! store it
+
+ /* Cross fingers and go for it. */
+ LOAD_WINDOW(sp)
+
+ /* A penny 'saved'... */
+ save %g0, %g0, %g0
+ save %g0, %g0, %g0
+ /* Is a BADTRAP earned... */
+
+ /* LOCATION: Window 'T' */
+
+LEON_PI(lda [%g0] ASI_LEON_MMUREGS, %twin_tmp1) ! load mmu-ctrl again
+SUN_PI_(lda [%g0] ASI_M_MMUREGS, %twin_tmp1) ! load mmu-ctrl again
+ andn %twin_tmp1, 0x2, %twin_tmp1 ! clear no-fault bit
+LEON_PI(sta %twin_tmp1, [%g0] ASI_LEON_MMUREGS) ! store it
+SUN_PI_(sta %twin_tmp1, [%g0] ASI_M_MMUREGS) ! store it
+
+ mov AC_M_SFAR, %twin_tmp2
+LEON_PI(lda [%twin_tmp2] ASI_LEON_MMUREGS, %g0) ! read fault address
+SUN_PI_(lda [%twin_tmp2] ASI_M_MMUREGS, %g0) ! read fault address
+
+ mov AC_M_SFSR, %twin_tmp2
+LEON_PI(lda [%twin_tmp2] ASI_LEON_MMUREGS, %twin_tmp2) ! read fault status
+SUN_PI_(lda [%twin_tmp2] ASI_M_MMUREGS, %twin_tmp2) ! read fault status
+ andcc %twin_tmp2, 0x2, %g0 ! did fault occur?
+
+ bne 1f ! yep, cleanup
+ nop
+
+ wr %t_psr, 0x0, %psr
+ nop
+ b fwin_user_finish_up + 0x4
+ nop
+
+ /* Did I ever tell you about my window lobotomy?
+ * anyways... fwin_user_stack_is_bolixed expects
+ * to be in window 'W' so make it happy or else
+ * we watchdog badly.
+ */
+1:
+ restore %g0, %g0, %g0
+ b fwin_user_stack_is_bolixed ! oh well
+ restore %g0, %g0, %g0