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

Christophe Leroy
2024-09-04T15:05:28Z

Le 04/09/2024 à 16:52, Arnd Bergmann a écrit :
> On Tue, Sep 3, 2024, at 15:14, Vincenzo Frascino wrote:
>
>> diff --git a/arch/x86/include/asm/vdso/page.h b/arch/x86/include/asm/vdso/page.h
>> new file mode 100644
>> index 000000000000..b0af8fbef27c
>> --- /dev/null
>> +++ b/arch/x86/include/asm/vdso/page.h
>> @@ -0,0 +1,15 @@
>> +
>> +/* 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.
>

Just wondering, after looking at x86, powerpc and arm64, is there any
difference between:

X86,ARM64:
#define PAGE_SIZE (_AC(1,UL) << PAGE_SHIFT)
#define PAGE_MASK (~(PAGE_SIZE-1))

POWERPC:
#define PAGE_SIZE (ASM_CONST(1) << PAGE_SHIFT)
/*
* Subtle: (1 << PAGE_SHIFT) is an int, not an unsigned long. So if we
* assign PAGE_MASK to a larger type it gets extended the way we want
* (i.e. with 1s in the high bits)
*/
#define PAGE_MASK (~((1 << PAGE_SHIFT) - 1))

Which one should be taken in vdso/page.h ?

Christophe