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

[Christophe Leroy]

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