source: mainline/kernel/arch/sparc64/src/start.S@ f1d1f5d3

#
# Copyright (C) 2005 Jakub Jermar
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#
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# modification, are permitted provided that the following conditions
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#include <arch/regdef.h>
#include <arch/boot/boot.h>

#include <arch/mm/mmu.h>
#include <arch/mm/tlb.h>
#include <arch/mm/tte.h>

.register %g2, #scratch
.register %g3, #scratch

.section K_TEXT_START, "ax"

/*
 * Here is where the kernel is passed control
 * from the boot loader.
 * 
 * The registers are expected to be in this state:
 * - %o0 bootinfo structure address
 * - %o1 bootinfo structure size
 *
 * Moreover, we depend on boot having established the
 * following environment:
 * - TLBs are on
 * - identity mapping for the kernel image
 * - identity mapping for memory stack
 */

.global kernel_image_start
kernel_image_start:

        /*
         * Setup basic runtime environment.
         */

        flushw                                  ! flush all but the active register window

        wrpr %g0, 0, %tl                        ! TL = 0, primary context register is used

        wrpr %g0, PSTATE_PRIV_BIT, %pstate      ! Disable interrupts and disable 32-bit address masking.

        wrpr %g0, 0, %pil                       ! intialize %pil

        /*
         * Copy the bootinfo structure passed from the boot loader
         * to the kernel bootinfo structure.
         */
        mov %o1, %o2
        mov %o0, %o1
        sethi %hi(bootinfo), %o0
        call memcpy
        or %o0, %lo(bootinfo), %o0

        /*
         * Switch to kernel trap table.
         */
        sethi %hi(trap_table), %g1
        wrpr %g1, %lo(trap_table), %tba

        /* 
         * Take over the DMMU by installing global locked
         * TTE entry identically mapping the first 4M
         * of memory.
         *
         * In case of DMMU, no FLUSH instructions need to be
         * issued. Because of that, the old DTLB contents can
         * be demapped pretty straightforwardly and without
         * causing any traps.
         */

        wr %g0, ASI_DMMU, %asi

#define SET_TLB_DEMAP_CMD(r1, context_id) \
        set (TLB_DEMAP_CONTEXT<<TLB_DEMAP_TYPE_SHIFT) | (context_id<<TLB_DEMAP_CONTEXT_SHIFT), %r1
        
        ! demap context 0
        SET_TLB_DEMAP_CMD(g1, TLB_DEMAP_NUCLEUS)
        stxa %g0, [%g1] ASI_DMMU_DEMAP                  
        membar #Sync

#define SET_TLB_TAG(r1, context) \
        set VMA | (context<<TLB_TAG_ACCESS_CONTEXT_SHIFT), %r1

        ! write DTLB tag
        SET_TLB_TAG(g1, MEM_CONTEXT_KERNEL)
        stxa %g1, [VA_DMMU_TAG_ACCESS] %asi                     
        membar #Sync

#define SET_TLB_DATA(r1, r2, imm) \
        set TTE_CV | TTE_CP | TTE_P | LMA | imm, %r1; \
        set PAGESIZE_4M, %r2; \
        sllx %r2, TTE_SIZE_SHIFT, %r2; \
        or %r1, %r2, %r1; \
        mov 1, %r2; \
        sllx %r2, TTE_V_SHIFT, %r2; \
        or %r1, %r2, %r1;
        
        ! write DTLB data and install the kernel mapping
        SET_TLB_DATA(g1, g2, TTE_L | TTE_W)     ! use non-global mapping
        stxa %g1, [%g0] ASI_DTLB_DATA_IN_REG            
        membar #Sync

        /*
         * Because we cannot use global mappings (because we want to
         * have separate 64-bit address spaces for both the kernel
         * and the userspace), we prepare the identity mapping also in
         * context 1. This step is required by the
         * code installing the ITLB mapping.
         */
        ! write DTLB tag of context 1 (i.e. MEM_CONTEXT_TEMP)
        SET_TLB_TAG(g1, MEM_CONTEXT_TEMP)
        stxa %g1, [VA_DMMU_TAG_ACCESS] %asi                     
        membar #Sync

        ! write DTLB data and install the kernel mapping in context 1
        SET_TLB_DATA(g1, g2, TTE_W)                     ! use non-global mapping
        stxa %g1, [%g0] ASI_DTLB_DATA_IN_REG            
        membar #Sync
        
        /*
         * Now is time to take over the IMMU.
         * Unfortunatelly, it cannot be done as easily as the DMMU,
         * because the IMMU is mapping the code it executes.
         *
         * [ Note that brave experiments with disabling the IMMU
         * and using the DMMU approach failed after a dozen
         * of desparate days with only little success. ]
         *
         * The approach used here is inspired from OpenBSD.
         * First, the kernel creates IMMU mapping for itself
         * in context 1 (MEM_CONTEXT_TEMP) and switches to
         * it. Context 0 (MEM_CONTEXT_KERNEL) can be demapped
         * afterwards and replaced with the kernel permanent
         * mapping. Finally, the kernel switches back to
         * context 0 and demaps context 1.
         *
         * Moreover, the IMMU requires use of the FLUSH instructions.
         * But that is OK because we always use operands with
         * addresses already mapped by the taken over DTLB.
         */
        
        set kernel_image_start, %g5
        
        ! write ITLB tag of context 1
        SET_TLB_TAG(g1, MEM_CONTEXT_TEMP)
        mov VA_DMMU_TAG_ACCESS, %g2
        stxa %g1, [%g2] ASI_IMMU
        flush %g5

        ! write ITLB data and install the temporary mapping in context 1
        SET_TLB_DATA(g1, g2, 0)                 ! use non-global mapping
        stxa %g1, [%g0] ASI_ITLB_DATA_IN_REG            
        flush %g5
        
        ! switch to context 1
        mov MEM_CONTEXT_TEMP, %g1
        stxa %g1, [VA_PRIMARY_CONTEXT_REG] %asi ! ASI_DMMU is correct here !!!
        flush %g5
        
        ! demap context 0
        SET_TLB_DEMAP_CMD(g1, TLB_DEMAP_NUCLEUS)
        stxa %g0, [%g1] ASI_IMMU_DEMAP                  
        flush %g5
        
        ! write ITLB tag of context 0
        SET_TLB_TAG(g1, MEM_CONTEXT_KERNEL)
        mov VA_DMMU_TAG_ACCESS, %g2
        stxa %g1, [%g2] ASI_IMMU
        flush %g5

        ! write ITLB data and install the permanent kernel mapping in context 0
        SET_TLB_DATA(g1, g2, TTE_L)             ! use non-global mapping
        stxa %g1, [%g0] ASI_ITLB_DATA_IN_REG            
        flush %g5

        ! switch to context 0
        stxa %g0, [VA_PRIMARY_CONTEXT_REG] %asi ! ASI_DMMU is correct here !!!
        flush %g5

        ! ensure nucleus mapping
        wrpr %g0, 1, %tl

        ! set context 1 in the primary context register
        mov MEM_CONTEXT_TEMP, %g1
        stxa %g1, [VA_PRIMARY_CONTEXT_REG] %asi ! ASI_DMMU is correct here !!!
        flush %g5

        ! demap context 1
        SET_TLB_DEMAP_CMD(g1, TLB_DEMAP_PRIMARY)
        stxa %g0, [%g1] ASI_IMMU_DEMAP                  
        flush %g5
        
        ! set context 0 in the primary context register
        stxa %g0, [VA_PRIMARY_CONTEXT_REG] %asi ! ASI_DMMU is correct here !!!
        flush %g5
        
        ! set TL back to 0
        wrpr %g0, 0, %tl

        call arch_pre_main
        nop
        
        call main_bsp
        nop

        /* Not reached. */

2:
        b 2b
        nop