[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20160111160906.GO6499@leverpostej>
Date: Mon, 11 Jan 2016 16:09:06 +0000
From: Mark Rutland <mark.rutland@....com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com, will.deacon@....com,
catalin.marinas@....com, leif.lindholm@...aro.org,
keescook@...omium.org, linux-kernel@...r.kernel.org,
stuart.yoder@...escale.com, bhupesh.sharma@...escale.com,
arnd@...db.de, marc.zyngier@....com, christoffer.dall@...aro.org
Subject: Re: [PATCH v3 04/21] arm64: decouple early fixmap init from linear
mapping
On Mon, Jan 11, 2016 at 02:18:57PM +0100, Ard Biesheuvel wrote:
> Since the early fixmap page tables are populated using pages that are
> part of the static footprint of the kernel, they are covered by the
> initial kernel mapping, and we can refer to them without using __va/__pa
> translations, which are tied to the linear mapping.
>
> Since the fixmap page tables are disjoint from the kernel mapping up
> to the top level pgd entry, we can refer to bm_pte[] directly, and there
> is no need to walk the page tables and perform __pa()/__va() translations
> at each step.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
> arch/arm64/mm/mmu.c | 32 ++++++--------------
> 1 file changed, 9 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 7711554a94f4..75b5f0dc3bdc 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -570,38 +570,24 @@ void vmemmap_free(unsigned long start, unsigned long end)
> #endif /* CONFIG_SPARSEMEM_VMEMMAP */
>
> static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
> -#if CONFIG_PGTABLE_LEVELS > 2
> static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
> -#endif
> -#if CONFIG_PGTABLE_LEVELS > 3
> static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
> -#endif
>
> static inline pud_t * fixmap_pud(unsigned long addr)
> {
> - pgd_t *pgd = pgd_offset_k(addr);
> -
> - BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd));
> -
> - return pud_offset(pgd, addr);
> + return (CONFIG_PGTABLE_LEVELS > 3) ? &bm_pud[pud_index(addr)]
> + : (pud_t *)pgd_offset_k(addr);
If we move patch 6 earlier, we could use pud_offset_kimg here, and avoid
the cast, at the cost of passing the pgd into fixmap_pud.
Similarly for fixmap_pmd.
> }
>
> -static inline pmd_t * fixmap_pmd(unsigned long addr)
> +static inline pte_t * fixmap_pmd(unsigned long addr)
> {
> - pud_t *pud = fixmap_pud(addr);
> -
> - BUG_ON(pud_none(*pud) || pud_bad(*pud));
> -
> - return pmd_offset(pud, addr);
> + return (CONFIG_PGTABLE_LEVELS > 2) ? &bm_pmd[pmd_index(addr)]
> + : (pmd_t *)pgd_offset_k(addr);
> }
I assume the return type change was unintentional?
With STRICT_MM_TYPECHECKS:
arch/arm64/mm/mmu.c: In function 'fixmap_pmd':
arch/arm64/mm/mmu.c:604:9: warning: return from incompatible pointer type [-Wincompatible-pointer-types]
return (CONFIG_PGTABLE_LEVELS > 2) ? &bm_pmd[pmd_index(addr)]
^
arch/arm64/mm/mmu.c: In function 'early_fixmap_init':
arch/arm64/mm/mmu.c:635:6: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
pmd = fixmap_pmd(addr);
^
arch/arm64/mm/mmu.c:645:11: warning: comparison of distinct pointer types lacks a cast
if ((pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
^
arch/arm64/mm/mmu.c:646:14: warning: comparison of distinct pointer types lacks a cast
|| pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
^
Side note: is there any reason we can't/shouldn't make
STRICT_MM_TYPECHECKS a common config option? Or simply have it on by
default for arm64?
Having built with and without typechecks I see that it doesn't bloat the
kernel Image size, though the binary isn't quite identical:
[mark@...erpostej:~/src/linux]% ls -al *.*checks
-rwxrwxr-x 1 mark mark 9288192 Jan 11 15:40 Image.checks
-rwxrwxr-x 1 mark mark 9288192 Jan 11 15:36 Image.nochecks
-rwxrwxr-x 1 mark mark 106782024 Jan 11 15:40 vmlinux.checks
-rwxrwxr-x 1 mark mark 106688928 Jan 11 15:35 vmlinux.nochecks
Things didn't quite line up between the two images, though I'm not sure
what the underlying difference was.
Thanks,
Mark.
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
