From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934252AbcAKRJA (ORCPT ); Mon, 11 Jan 2016 12:09:00 -0500 Received: from mail-io0-f175.google.com ([209.85.223.175]:34141 "EHLO mail-io0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758558AbcAKRI6 (ORCPT ); Mon, 11 Jan 2016 12:08:58 -0500 MIME-Version: 1.0 In-Reply-To: <20160111165103.GA29503@leverpostej> References: <1452518355-4606-1-git-send-email-ard.biesheuvel@linaro.org> <1452518355-4606-5-git-send-email-ard.biesheuvel@linaro.org> <20160111160906.GO6499@leverpostej> <20160111162737.GQ6499@leverpostej> <20160111165103.GA29503@leverpostej> Date: Mon, 11 Jan 2016 18:08:57 +0100 Message-ID: Subject: Re: [PATCH v3 04/21] arm64: decouple early fixmap init from linear mapping From: Ard Biesheuvel To: Mark Rutland Cc: Kees Cook , Arnd Bergmann , kernel-hardening@lists.openwall.com, Sharma Bhupesh , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Leif Lindholm , Stuart Yoder , Marc Zyngier , Christoffer Dall , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11 January 2016 at 17:51, Mark Rutland wrote: > On Mon, Jan 11, 2016 at 04:27:38PM +0000, Mark Rutland wrote: >> On Mon, Jan 11, 2016 at 05:15:13PM +0100, Ard Biesheuvel wrote: >> > On 11 January 2016 at 17:09, Mark Rutland wrote: >> > > 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 >> > >> --- >> > >> 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. >> > > >> > >> > Is that necessarily an improvement? I know it hides the cast, but I >> > think having an explicit pgd_t* to pud_t* cast that so obviously >> > applies to CONFIG_PGTABLE_LEVELS < 4 only is fine as well. >> >> True; it's not a big thing either way. > > Sorry, I'm gonig to change my mind on that again. I think using > p?d_offset_kimg is preferable. e.g. > > 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_kimg(pgd, addr); > } > > static inline pmd_t * fixmap_pmd(unsigned long addr) > { > pud_t *pud = fixmap_pud(addr); > > BUG_ON(pud_none(*pud) || pud_bad(*pud)); > > return pmd_offset_kimg(pud, addr); > } > > That avoids having to check CONFIG_PGTABLE_LEVELS check and perform a cast, > avoids duplicating details about bm_{pud,pmd}, and keeps the existing structure > so it's easier to reason about the change. I was wrong about having to pass the > pgd or pud in, so callers don't need upating. > > From my PoV that is preferable. > OK. I think it looks better, indeed.