linux-kernel - Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for NO

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Message-ID: <alpine.DEB.2.21.1809161633160.1650@nanos.tec.linutronix.de>
Date:   Sun, 16 Sep 2018 16:43:55 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Feng Tang <feng.tang@...el.com>
cc:     Michal Hocko <mhocko@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Ingo Molnar <mingo@...e.hu>,
        "H . Peter Anvin" <hpa@...ux.intel.com>,
        Yinghai Lu <yinghai@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for
 NO_BOOTMEM

On Sun, 16 Sep 2018, Feng Tang wrote:
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index e848a4811785..a927f5f39bee 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -637,6 +637,16 @@ void __native_set_fixmap(enum fixed_addresses idx, pte_t pte)
>  {
>  	unsigned long address = __fix_to_virt(idx);
>  
> +#ifdef CONFIG_X86_64
> +       /*
> +        * In arch/x86/kernel/head_64.S, the static page table has
> +	* been setup for fixmap. Add a sanity compiling check
> +	* whether fixmap space has exceeded the capacity.
> +        */
> +       BUILD_BUG_ON((__end_of_permanent_fixed_addresses + 511)/512
> +                       > FIXMAP_PMD_NUM);

There exist macros for rounding up and doing this in the header file is
perfectly fine.

> +#endif
> +
>  	if (idx >= __end_of_fixed_addresses) {
>  		BUG();
>  		return;
> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> index 45b700ac5fe7..b0aa2364a3c6 100644
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -1953,7 +1953,10 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
>  	set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO);
>  	set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
>  	set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO);
> -	set_page_prot(level1_fixmap_pgt, PAGE_KERNEL_RO);
> +
> +	for (i = 0; i < FIXMAP_PMD_NUM; i++)
> +		set_page_prot(level1_fixmap_pgt + i * 512,
> +				PAGE_KERNEL_RO);

The line break is there because?

Thanks,

	tglx