Re: [PATCH 12/16] x86/mm/pae: Populate the user page-table with user pgd's

[Thomas Gleixner]

On Tue, 16 Jan 2018, Joerg Roedel wrote:
>  
> +#ifdef CONFIG_X86_64
>  	/*
>  	 * If this is normal user memory, make it NX in the kernel
>  	 * pagetables so that, if we somehow screw up and return to
> @@ -134,10 +135,16 @@ pgd_t __pti_set_user_pgd(pgd_t *pgdp, pgd_t pgd)
>  	 *     may execute from it
>  	 *  - we don't have NX support
>  	 *  - we're clearing the PGD (i.e. the new pgd is not present).
> +	 *  - We run on a 32 bit kernel. 2-level paging doesn't support NX at
> +	 *    all and PAE paging does not support it on the PGD level. We can
> +	 *    set it in the PMD level there in the future, but that means we
> +	 *    need to unshare the PMDs between the kernel and the user
> +	 *    page-tables.
>  	 */
>  	if ((pgd.pgd & (_PAGE_USER|_PAGE_PRESENT)) == (_PAGE_USER|_PAGE_PRESENT) &&
>  	    (__supported_pte_mask & _PAGE_NX))
>  		pgd.pgd |= _PAGE_NX;

I'd suggest to have:

static inline pteval_t supported_pgd_mask(void)
{
	if (IS_ENABLED(CONFIG_X86_64))
		return __supported_pte_mask;
	return __supported_pte_mask & ~_PAGE_NX);
}

and get rid of the ifdeffery completely.

Thanks,

	tglx