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b=USTJwMyGvWXoMbf/S3Hkuw/RAJZlgHz1wf6Rv3/jmc2THf0cyKGDOtGKt9FmAlIO2 bEzFbeCt0rnDn/8rlPAlmhLya/lie2fE7s0Ml45wXgkLiE48k3nYrM5tUD//wtZoUe Or1W+w7erYiqub4kaHP0qkQb3RECfdmHprx1Vj3YKxor8X2FJMM9b4kv+OtRUUTLhY dmdFE+f1EYTQmxHd5kFze5j7kVMcZ/PDIzwqvicbpyNpYnweMPLgb8vUH92a7Ecsu/ AQ6G7A7Ro/8u63LF4IMK8XJnfB3/MXr6DrdO23eJ8HfBnbe96tH4zBoN13i1Sk2LFH iU1t+RcUX53pg== Date: Thu, 28 May 2026 08:46:04 +0300 From: Mike Rapoport To: Ard Biesheuvel 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 , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , David Hildenbrand , Andrew Morton , Jann Horn , linux-mm@kvack.org, linux-hardening@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz Subject: Re: [PATCH v6 13/15] sh: cast away constness from the zero page when flushing it from the cache Message-ID: References: <20260526175846.2694125-17-ardb+git@google.com> <20260526175846.2694125-30-ardb+git@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260526175846.2694125-30-ardb+git@google.com> X-Stat-Signature: 4p7qzqijdfq4jfujdmdkwckzrtc7traz X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D29E4100003 X-Rspam-User: X-HE-Tag: 1779947174-884381 X-HE-Meta: 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 Dm1dlRkA trcvDWGfY3/UNdzSLg1/tSrNvo03IYrDEJ9A1GXIgaEjyfczMat49EKdKbrj58BIvgeP/LQP06cFp7dKiucg1k3ycSa0l++bs/5cjWnNk7eAT7+iWYFER1qDFthZSB/uR86FklA/R0vH4TrZeerxOwyZvxhTgZE5f3wjYDA0iAenn3wuF0drheT+6OYZC0L3JKMZKDNagqQK5J0UU6va7tdHvW7vVpvnUbHncHSkPP4FXQwnHUFQgRJ8Vt3y3b7g86T90haega5Mailx0xPtUrweywxkz6pa8ITrH0FaBK/TG85ifL0o79XGhzMrM07LKfvCFqkH5AwUyA3/djioiGX6r8RmmVHd5d4sCFuptFc+c2HeZoHHYcpSRN7vTUZDmLXWOxdmRIZEoN1eEKPCIJa3Z5KDzxEKEBXJP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 26, 2026 at 07:59:00PM +0200, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > 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 > Cc: Rich Felker > Cc: John Paul Adrian Glaubitz > Signed-off-by: Ard Biesheuvel > --- > 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.