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SubjectRe: [PATCH 09/16] x86/mm/pti: Clone CPU_ENTRY_AREA on PMD level on x86_32
On Tue, 16 Jan 2018, Joerg Roedel wrote:
> +#ifdef CONFIG_X86_64
> /*
> * Clone a single p4d (i.e. a top-level entry on 4-level systems and a
> * next-level entry on 5-level systems.
> @@ -322,13 +323,29 @@ static void __init pti_clone_p4d(unsigned long addr)
> kernel_p4d = p4d_offset(kernel_pgd, addr);
> *user_p4d = *kernel_p4d;
> }
> +#endif
>
> /*
> * Clone the CPU_ENTRY_AREA into the user space visible page table.
> */
> static void __init pti_clone_user_shared(void)
> {
> +#ifdef CONFIG_X86_32
> + /*
> + * On 32 bit PAE systems with 1GB of Kernel address space there is only
> + * one pgd/p4d for the whole kernel. Cloning that would map the whole
> + * address space into the user page-tables, making PTI useless. So clone
> + * the page-table on the PMD level to prevent that.
> + */
> + unsigned long start, end;
> +
> + start = CPU_ENTRY_AREA_BASE;
> + end = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES);
> +
> + pti_clone_pmds(start, end, _PAGE_GLOBAL);
> +#else
> pti_clone_p4d(CPU_ENTRY_AREA_BASE);
> +#endif
> }

Just a minor nit. You already wrap pti_clone_p4d() into X86_64. So it would
be cleaner to do:

kernel_p4d = p4d_offset(kernel_pgd, addr);
*user_p4d = *kernel_p4d;
}

static void __init pti_clone_user_shared(void)
{
pti_clone_p4d(CPU_ENTRY_AREA_BASE);
}

#else /* CONFIG_X86_64 */

/*
* Big fat comment.
*/
static void __init pti_clone_user_shared(void)
{
....
}
#endif /* !CONFIG_X86_64 */

Thanks,

tglx

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