Re: [PATCH v3 11/20] arm64: mm: Map entry trampoline into trampoline and kernel page tables

Yisheng Xie
2018-01-23T08:29:21Z

Hi Will,

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.

Thanks
Yisheng

> +
> + /* ...as well as the kernel page table */
> + __set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot);
> + return 0;
> +}
> +core_initcall(map_entry_trampoline);
> +#endif
> +
> /*
> * Create fine-grained mappings for the kernel.
> */
>