linux-kernel - Re: [PATCH v3 2/2] vdso: Introduce vdso/page.h

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Message-Id: <423e571b-3ef6-4e80-ba81-bf42589a4ba8@app.fastmail.com>
Date: Fri, 04 Oct 2024 13:13:46 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Vincenzo Frascino" <vincenzo.frascino@....com>,
 linux-kernel@...r.kernel.org, Linux-Arch <linux-arch@...r.kernel.org>,
 linux-mm@...ck.org
Cc: "Andy Lutomirski" <luto@...nel.org>,
 "Thomas Gleixner" <tglx@...utronix.de>,
 "Jason A . Donenfeld" <Jason@...c4.com>,
 "Christophe Leroy" <christophe.leroy@...roup.eu>,
 "Michael Ellerman" <mpe@...erman.id.au>,
 "Nicholas Piggin" <npiggin@...il.com>, "Naveen N Rao" <naveen@...nel.org>,
 "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, "Theodore Ts'o" <tytso@....edu>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Steven Rostedt" <rostedt@...dmis.org>,
 "Masami Hiramatsu" <mhiramat@...nel.org>,
 "Mathieu Desnoyers" <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH v3 2/2] vdso: Introduce vdso/page.h

On Thu, Oct 3, 2024, at 15:29, Vincenzo Frascino wrote:
> The VDSO implementation includes headers from outside of the
> vdso/ namespace.
>
> Introduce vdso/page.h to make sure that the generic library
> uses only the allowed namespace.
>
> Note: on a 32-bit architecture UL is an unsigned 32 bit long. Hence when
> it supports 64-bit phys_addr_t we might end up in situation in which the
> top 32 bit are cleared. To prevent this issue this patch provides
> separate macros for PAGE_MASK.
>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Jason A. Donenfeld <Jason@...c4.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>

Looks good to me. I would apply this to the asm-generic
tree for 6.13, but there is one small detail I'm unsure
about:

> +#if defined(CONFIG_PHYS_ADDR_T_64BIT)
> +#define PAGE_MASK	(~((1 << CONFIG_PAGE_SHIFT) - 1))
> +#else
> +#define PAGE_MASK	(~(PAGE_SIZE-1))
> +#endif

We only want the #if branch for 32-bit architectures, right?

On 64-bit ones, CONFIG_PHYS_ADDR_T_64BIT is always set, so
I think that is unnecessary change from the existing version,
even though it should be harmless.

     Arnd