Re: [tip:x86/vdso] x86/arch_prctl/vdso: Add ARCH_MAP_VDSO_*

[Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>]

On 10/26/2016 03:30 PM, Paul Bolle wrote:
> This is bit late, but we're still on v4.9-rc2, so anyhow.
>
> On Wed, 2016-09-14 at 12:34 -0700, tip-bot for Dmitry Safonov wrote:
> > Commit-ID:  2eefd8789698e89c4a5d610921dc3c1b66e3bd0d
> > Gitweb:     http://git.kernel.org/tip/2eefd8789698e89c4a5d610921dc3c1b66e3bd0d
> > Author:     Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
> > AuthorDate: Mon, 5 Sep 2016 16:33:05 +0300
> > Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > CommitDate: Wed, 14 Sep 2016 21:28:09 +0200
> >
> > x86/arch_prctl/vdso: Add ARCH_MAP_VDSO_*
> >
> > Add API to change vdso blob type with arch_prctl.
> > As this is usefull only by needs of CRIU, expose
> > this interface under CONFIG_CHECKPOINT_RESTORE.
> >
> > Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
> > Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > Cc: 0x7f454c46@xxxxxxxxx
> > Cc: oleg@xxxxxxxxxx
> > Cc: linux-mm@xxxxxxxxx
> > Cc: gorcunov@xxxxxxxxxx
> > Cc: xemul@xxxxxxxxxxxxx
> > Link: http://lkml.kernel.org/r/20160905133308.28234-4-dsafonov@xxxxxxxxxxxxx
> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>
> > --- a/arch/x86/include/uapi/asm/prctl.h
> > +++ b/arch/x86/include/uapi/asm/prctl.h
>
> >  #define ARCH_GET_FS 0x1003
> >  #define ARCH_GET_GS 0x1004
> >
> > +#ifdef CONFIG_CHECKPOINT_RESTORE
> > +# define ARCH_MAP_VDSO_X32	0x2001
> > +# define ARCH_MAP_VDSO_32	0x2002
> > +# define ARCH_MAP_VDSO_64	0x2003
> > +#endif
> > +
> >  #endif /* _ASM_X86_PRCTL_H */
>
> On my machine this header ends up in /usr/include/asm/prctl.h. But in
> userspace CONFIG_CHECKPOINT_RESTORE is meaningless. I think if you
> actually want to export these three macros to userspace the guard
> should read:
>     #if defined(CONFIG_CHECKPOINT_RESTORE) || !defined(__KERNEL__)
>
> And if you don't want to export these macros the guard should read:
>     #if defined(CONFIG_CHECKPOINT_RESTORE) && defined(__KERNEL__)
>
> (In that case you're probably better of defining these macros outside
> of uapi.)
>
> I've only lightly tested those two alternatives, so please double
> check.

Hi Paul,

thanks for noting that!
Well, I think, I'll remove ifdeffery around those constants.
Let them be always defined, that would be the simplest solution.
Somehow I managed to forget that userspace knows nothing about enabled
kernel options.

Thanks again,
            Dmitry

> Paul Bolle
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