linux-kernel - Re: [PATCH 2/4] random: vDSO: Don't use PAGE_SIZE and PAGE

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Message-ID: <Zs2FJku2hM2bp4ik@zx2c4.com>
Date: Tue, 27 Aug 2024 09:49:58 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Theodore Ts'o <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
	Andy Lutomirski <luto@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 2/4] random: vDSO: Don't use PAGE_SIZE and PAGE_MASK

On Tue, Aug 27, 2024 at 09:31:48AM +0200, Christophe Leroy wrote:
> -	ssize_t ret = min_t(size_t, INT_MAX & PAGE_MASK /* = MAX_RW_COUNT */, len);
> +	const unsigned long page_size = 1UL << CONFIG_PAGE_SHIFT;
> +	const unsigned long page_mask = ~(page_size - 1);
> +	ssize_t ret = min_t(size_t, INT_MAX & page_mask /* = MAX_RW_COUNT */, len);

I'm really not a fan of making the code less idiomatic...

> An easy solution would be to define PAGE_SIZE and PAGE_MASK in vDSO
> when they do not exist already, but this can be misleading.

Why would what tglx and I suggested be misleading? That seems pretty
normal... Are you worried they might mismatch somehow? (If so, why?) 

Jason