[Xen-devel] Why we are doing this (below code) in __init setup_pagetables() method in ARM arch in setup.c.

[asad raza <asadrupucit2006@xxxxxxxxx>]

 /* Link in the fixmap pagetable */
    pte = mfn_to_xen_entry((((unsigned long) xen_fixmap) + phys_offset)
                           >> PAGE_SHIFT);
    pte.pt.table = 1;
    write_pte(xen_second + second_table_offset(FIXMAP_ADDR(0)), pte);
    /*
     * No flush required here. Individual flushes are done in
     * set_fixmap as entries are used.
     */

    /* Break up the Xen mapping into 4k pages and protect them separately. */
    for ( i = 0; i < LPAE_ENTRIES; i++ )
    {
        unsigned long mfn = paddr_to_pfn(xen_paddr) + i;
        unsigned long va = XEN_VIRT_START + (i << PAGE_SHIFT);
        if ( !is_kernel(va) )
            break;
        pte = mfn_to_xen_entry(mfn);
        pte.pt.table = 1; /* 4k mappings always have this bit set */
        if ( is_kernel_text(va) || is_kernel_inittext(va) )
        {
            pte.pt.xn = 0;
            pte.pt.ro = 1;
        }
        if ( is_kernel_rodata(va) )
            pte.pt.ro = 1;
        write_pte(xen_xenmap + i, pte);
        /* No flush required here as page table is not hooked in yet. */
    }
    pte = mfn_to_xen_entry((((unsigned long) xen_xenmap) + phys_offset)
                           >> PAGE_SHIFT);
    pte.pt.table = 1;
    write_pte(xen_second + second_linear_offset(XEN_VIRT_START), pte);
    /* Have changed a mapping used for .text. Flush everything for safety. */
    flush_xen_text_tlb();

    /* From now on, no mapping may be both writable and executable. */
    WRITE_CP32(READ_CP32(HSCTLR) | SCTLR_WXN, HSCTLR);

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