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

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Date:   Tue, 23 Jan 2018 16:28:45 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     Will Deacon <will.deacon@....com>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     <linux-kernel@...r.kernel.org>, <catalin.marinas@....com>,
        <mark.rutland@....com>, <ard.biesheuvel@...aro.org>,
        <sboyd@...eaurora.org>, <dave.hansen@...ux.intel.com>,
        <keescook@...omium.org>, <msalter@...hat.com>,
        <labbott@...hat.com>, <tglx@...utronix.de>
Subject: Re: [PATCH v3 11/20] arm64: mm: Map entry trampoline into trampoline
 and kernel page tables

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.
>   */
>