From: Kevin Brodsky <kevin.brodsky@arm•com>
To: Ard Biesheuvel <ardb+git@google•com>,
linux-arm-kernel@lists•infradead.org
Cc: linux-kernel@vger•kernel.org, will@kernel•org,
catalin.marinas@arm•com, mark.rutland@arm•com,
Ard Biesheuvel <ardb@kernel•org>,
Ryan Roberts <ryan.roberts@arm•com>,
Anshuman Khandual <anshuman.khandual@arm•com>,
Liz Prucka <lizprucka@google•com>,
Seth Jenkins <sethjenkins@google•com>,
Kees Cook <kees@kernel•org>, Mike Rapoport <rppt@kernel•org>,
David Hildenbrand <david@kernel•org>,
Andrew Morton <akpm@linux-foundation•org>,
Jann Horn <jannh@google•com>,
linux-mm@kvack•org, linux-hardening@vger•kernel.org,
linuxppc-dev@lists•ozlabs.org, linux-sh@vger•kernel.org
Subject: Re: [PATCH v6 08/15] arm64: mm: Permit contiguous attribute for preliminary mappings
Date: Fri, 29 May 2026 10:25:39 +0200 [thread overview]
Message-ID: <9493da99-3476-4fdd-818b-19e424b46f8e@arm.com> (raw)
In-Reply-To: <20260526175846.2694125-25-ardb+git@google.com>
On 26/05/2026 19:58, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel•org>
>
> There are a few cases where we omit the contiguous hint for mappings
> that start out as read-write and are remapped read-only later, on the
> basis that manipulating live descriptors with the PTE_CONT attribute set
> is unsafe. When support for the contiguous hint was added to the code,
> the ARM ARM was ambiguous about this, and so we erred on the side of
> caution.
>
> In the meantime, this has been clarified [0], and regions that will be
> remapped in their entirety, retaining the contiguous bit on all entries,
> can use the contiguous hint both in the initial mapping as well as the
> one that replaces it. Note that this requires that the logic that may be
> called to remap overlapping regions respects existing valid descriptors
> that have the contiguous bit cleared.
>
> So omit the NO_CONT_MAPPINGS flag in places where it is unneeded.
>
> Thanks to Ryan for the reference.
>
> [0] RJQQTC
>
> For a TLB lookup in a contiguous region mapped by translation table entries that
> have consistent values for the Contiguous bit, but have the OA, attributes, or
> permissions misprogrammed, that TLB lookup is permitted to produce an OA, access
> permissions, and memory attributes that are consistent with any one of the
> programmed translation table values.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel•org>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm•com>
> ---
> arch/arm64/mm/mmu.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 55bb40348a47..04cc579c7a15 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1016,8 +1016,7 @@ void __init create_mapping_noalloc(phys_addr_t phys, unsigned long virt,
> &phys, virt);
> return;
> }
> - early_create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL,
> - NO_CONT_MAPPINGS);
> + early_create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, 0);
> }
>
> void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
> @@ -1044,8 +1043,7 @@ static void update_mapping_prot(phys_addr_t phys, unsigned long virt,
> return;
> }
>
> - early_create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL,
> - NO_CONT_MAPPINGS);
> + early_create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, 0);
>
> /* flush the TLBs after updating live kernel mappings */
> flush_tlb_kernel_range(virt, virt + size);
> @@ -1191,10 +1189,8 @@ static void __init map_mem(void)
> * alternative patching has completed). This makes the contents
> * of the region accessible to subsystems such as hibernate,
> * but protects it from inadvertent modification or execution.
> - * Note that contiguous mappings cannot be remapped in this way,
> - * so we should avoid them here.
> */
> - __map_memblock(kernel_start, kernel_end, PAGE_KERNEL, NO_CONT_MAPPINGS);
> + __map_memblock(kernel_start, kernel_end, PAGE_KERNEL, 0);
> memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
> }
>
next prev parent reply other threads:[~2026-05-29 8:25 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-26 17:58 [PATCH v6 00/15] arm64: Unmap linear alias of kernel data/bss Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 01/15] arm64: mm: Remove bogus stop condition from map_mem() loop Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 02/15] arm64: mm: Drop redundant pgd_t* argument from map_mem() Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 03/15] arm64: mm: Check for pud_/pmd_set_huge() failures on kernel mappings Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 04/15] arm64: mm: Preserve existing table mappings when mapping DRAM Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 05/15] arm64: mm: Preserve non-contiguous descriptors " Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 06/15] arm64: mm: Permit contiguous descriptors to be manipulated Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 07/15] arm64: kfence: Avoid NOMAP tricks when mapping the early pool Ard Biesheuvel
2026-05-29 8:25 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 08/15] arm64: mm: Permit contiguous attribute for preliminary mappings Ard Biesheuvel
2026-05-29 8:25 ` Kevin Brodsky [this message]
2026-05-26 17:58 ` [PATCH v6 09/15] arm64: Move fixmap and kasan page tables to end of kernel image Ard Biesheuvel
2026-05-29 8:27 ` Kevin Brodsky
2026-05-29 11:19 ` Ard Biesheuvel
2026-05-29 14:42 ` Kevin Brodsky
2026-05-29 14:47 ` Ard Biesheuvel
2026-06-01 8:37 ` Kevin Brodsky
2026-06-01 8:39 ` Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 10/15] arm64: mm: Don't abuse memblock NOMAP to check for overlaps Ard Biesheuvel
2026-05-29 8:28 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 11/15] arm64: mm: Map the kernel data/bss read-only in the linear map Ard Biesheuvel
2026-05-29 8:28 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 12/15] powerpc/code-patching: Avoid r/w mapping of the zero page Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 13/15] sh: cast away constness from the zero page when flushing it from the cache Ard Biesheuvel
2026-05-27 9:31 ` Geert Uytterhoeven
2026-05-28 5:46 ` Mike Rapoport
2026-05-28 6:14 ` Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 14/15] mm: Make empty_zero_page[] const Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 15/15] arm64: mm: Unmap kernel data/bss entirely from the linear map Ard Biesheuvel
2026-05-29 8:29 ` Kevin Brodsky
2026-05-29 8:34 ` Ard Biesheuvel
2026-05-29 8:49 ` Kevin Brodsky
2026-05-29 11:48 ` Ard Biesheuvel
2026-05-29 8:31 ` [PATCH v6 00/15] arm64: Unmap linear alias of kernel data/bss Kevin Brodsky
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