Messages in this thread | | | Date | Tue, 23 Jan 2018 10:04:47 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v3 11/20] arm64: mm: Map entry trampoline into trampoline and kernel page tables |
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On Tue, Jan 23, 2018 at 04:28:45PM +0800, Yisheng Xie wrote: > On 2017/12/6 20:35, Will Deacon wrote: > > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > > +static int __init map_entry_trampoline(void) > > +{ > > + extern char __entry_tramp_text_start[]; > > + > > + pgprot_t prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC; > > + phys_addr_t pa_start = __pa_symbol(__entry_tramp_text_start); > > + > > + /* The trampoline is always mapped and can therefore be global */ > > + pgprot_val(prot) &= ~PTE_NG; > > + > > + /* Map only the text into the trampoline page table */ > > + memset(tramp_pg_dir, 0, PGD_SIZE); > > + __create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE, > > + prot, pgd_pgtable_alloc, 0); > > How the tramp_pg_dir is used, should it be set to ttbr1 when exit kernel? Sorry > for I do not find where it is used.
Yes, that's what happens when we return to userspace. The code is a little convoluted, but the tramp_pg_dir is placed at a fixed offset from swapper (see the linker script) so the sub instruction in tramp_unmap_kernel is what gives us the ttbr1 value we need.
Will
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