From: Mike Rapoport <rppt@kernel•org>
To: Ard Biesheuvel <ardb+git@google•com>
Cc: linux-arm-kernel@lists•infradead.org,
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>, 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,
Yoshinori Sato <ysato@users•sourceforge.jp>,
Rich Felker <dalias@libc•org>,
John Paul Adrian Glaubitz <glaubitz@physik•fu-berlin.de>
Subject: Re: [PATCH v6 13/15] sh: cast away constness from the zero page when flushing it from the cache
Date: Thu, 28 May 2026 08:46:04 +0300 [thread overview]
Message-ID: <ahfWnLIwZXJvbvNg@kernel.org> (raw)
In-Reply-To: <20260526175846.2694125-30-ardb+git@google.com>
On Tue, May 26, 2026 at 07:59:00PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel•org>
>
> SH performs cache maintenance on the zero page during boot, presumably
> to ensure that any clearing of BSS that has occurred at startup is
> visible to other CPUs and DMA devices.
It flushes the cache there because before 6215d9f4470f ("arch, mm:
consolidate empty_zero_page") empty_zero_page used was for boot parameters
at the very early boot.
I removed memset(empty_zero_page, 0, PAGE_SIZE) that was a line above but
missed the cache flush.
This whole "clear zero-page" can be removed IMO.
> The __flush_wback_region() function takes a void* argument, which is
> conceptually sound, but given that empty_zero_page[] must never be
> modified, it is being repainted as const, making it incompatible with a
> void* formal parameter.
>
> Given the above, and the fact that __flush_wback_region() is in fact a
> function pointer variable with multiple implementations, take the easy
> way out, and cast away the constness in this particular invocation.
>
> Cc: Yoshinori Sato <ysato@users•sourceforge.jp>
> Cc: Rich Felker <dalias@libc•org>
> Cc: John Paul Adrian Glaubitz <glaubitz@physik•fu-berlin.de>
> Signed-off-by: Ard Biesheuvel <ardb@kernel•org>
> ---
> arch/sh/mm/init.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
> index 4e40d5e96be9..acbb481cdbfe 100644
> --- a/arch/sh/mm/init.c
> +++ b/arch/sh/mm/init.c
> @@ -332,7 +332,7 @@ void __init mem_init(void)
> cpu_cache_init();
>
> /* clear the zero-page */
> - __flush_wback_region(empty_zero_page, PAGE_SIZE);
> + __flush_wback_region((void *)empty_zero_page, PAGE_SIZE);
>
> vsyscall_init();
>
> --
> 2.54.0.794.g4f17f83d09-goog
>
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2026-05-28 5:46 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
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 [this message]
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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