linux-kernel - Re: [PATCH 3/9] x86: vdso: Introduce asm/vdso/page.h

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Message-ID: <e28e1974-cced-462c-8f57-ca1474272e73@arm.com>
Date: Fri, 6 Sep 2024 12:20:31 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: Arnd Bergmann <arnd@...db.de>, 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 3/9] x86: vdso: Introduce asm/vdso/page.h

Hi Arnd,

On 04/09/2024 15:52, Arnd Bergmann wrote:
> On Tue, Sep 3, 2024, at 15:14, Vincenzo Frascino wrote:
> 

...

>> +
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef __ASM_VDSO_PAGE_H
>> +#define __ASM_VDSO_PAGE_H
>> +
>> +#ifndef __ASSEMBLY__
>> +
>> +#include <asm/page_types.h>
>> +
>> +#define VDSO_PAGE_MASK	PAGE_MASK
>> +#define VDSO_PAGE_SIZE	PAGE_SIZE
>> +
>> +#endif /* !__ASSEMBLY__ */
>> +
>> +#endif /* __ASM_VDSO_PAGE_H */
> 
> I don't get this one: the x86 asm/page_types.h still includes other
> headers outside of the vdso namespace, but you seem to only need these
> two definitions that are the same across everything.
> > Why not put PAGE_MASK and PAGE_SIZE into a global vdso/page.h
> header? I did spend a lot of time a few months ago ensuring that
> we can have a single definition for all architectures based on
> CONFIG_PAGE_SHIFT, so all the extra copies should just go away.
> 
>        Arnd
Looking at the definition of PAGE_SIZE and PAGE_MASK for each architecture they
all depend on CONFIG_PAGE_SHIFT but they are slightly different, e.g.:

x86:
#define PAGE_SIZE        (_AC(1,UL) << PAGE_SHIFT)

powerpc:
#define PAGE_SIZE        (ASM_CONST(1) << PAGE_SHIFT)

hence I left to the architecture the responsibility of redefining the constants
for the VSDO.

As a long term plan I would like to simplify the code and have a single
definition as you are saying in vdso/page.h for both the macros. But my
preference would be to post it as a separate series so that I can focus more on
validating it properly.

-- 
Regards,
Vincenzo