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

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Message-ID: <850cdc2a-a336-4dab-bc7a-d9bcae3fb3cf@arm.com>
Date: Mon, 7 Oct 2024 12:01:04 +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 v3 2/2] vdso: Introduce vdso/page.h

On 04/10/2024 14:13, Arnd Bergmann wrote:
> 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:
>

Thanks.

>> +#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.
> 

It seemed harmless from the tests I did. But adding an '&&
defined(CONFIG_32BIT)' makes it logically correct. I will add a comment as well
in the next version.

>      Arnd

-- 
Regards,
Vincenzo