linux-kernel - Re: [tip:x86/boot] x86/boot: Micro-optimize reset_early_page

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Date:	Thu, 4 Feb 2016 16:25:32 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	luto@...nel.org, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	ryabinin.a.a@...il.com, Peter Zijlstra <peterz@...radead.org>,
	alpopov@...ecurity.com
Cc:	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/boot] x86/boot: Micro-optimize reset_early_page_tables()

On Sat, Jan 30, 2016 at 12:26 AM, tip-bot for Alexander Kuleshov
<tipbot@...or.com> wrote:
> ---
>  arch/x86/kernel/head64.c | 14 +++-----------
>  1 file changed, 3 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index f129a9a..35843ca 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -40,13 +40,8 @@ pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);

.
>
> @@ -54,7 +49,6 @@ static void __init reset_early_page_tables(void)
>  int __init early_make_pgtable(unsigned long address)
>  {
>         unsigned long physaddr = address - __PAGE_OFFSET;
> -       unsigned long i;
>         pgdval_t pgd, *pgd_p;
>         pudval_t pud, *pud_p;
>         pmdval_t pmd, *pmd_p;
> @@ -81,8 +75,7 @@ again:
>                 }
>
>                 pud_p = (pudval_t *)early_dynamic_pgts[next_early_pgt++];
> -               for (i = 0; i < PTRS_PER_PUD; i++)
> -                       pud_p[i] = 0;
> +               memset(pud_p, 0, sizeof(pud_p) * PTRS_PER_PUD);

should be
                  memset(pud_p, 0, sizeof(*pud_p) * PTRS_PER_PUD);

>                 *pgd_p = (pgdval_t)pud_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
>         }
>         pud_p += pud_index(address);
> @@ -97,8 +90,7 @@ again:
>                 }
>
>                 pmd_p = (pmdval_t *)early_dynamic_pgts[next_early_pgt++];
> -               for (i = 0; i < PTRS_PER_PMD; i++)
> -                       pmd_p[i] = 0;
> +               memset(pmd_p, 0, sizeof(pmd_p) * PTRS_PER_PMD);

should be
                    memset(pmd_p, 0, sizeof(*pmd_p) * PTRS_PER_PMD);

>                 *pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
>         }
>         pmd = (physaddr & PMD_MASK) + early_pmd_flags;