Subject: Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits

From: Charlie Jenkins <[email-masked]>
Date: Mon, 9 Sep 2024 12:07:26 -0700

On Fri, Sep 06, 2024 at 04:59:40PM +1000, Michael Ellerman wrote:
> Charlie Jenkins <[email-masked]> writes:
> > Create a personality flag ADDR_LIMIT_47BIT to support applications
> > that wish to transition from running in environments that support at
> > most 47-bit VAs to environments that support larger VAs. This
> > personality can be set to cause all allocations to be below the 47-bit
> > boundary. Using MAP_FIXED with mmap() will bypass this restriction.
> >
> > Signed-off-by: Charlie Jenkins <[email-masked]>
> > ---
> >  include/uapi/linux/personality.h | 1 +
> >  mm/mmap.c                        | 3 +++
> >  2 files changed, 4 insertions(+)
> >
> > diff --git a/include/uapi/linux/personality.h b/include/uapi/linux/personality.h
> > index 49796b7756af..cd3b8c154d9b 100644
> > --- a/include/uapi/linux/personality.h
> > +++ b/include/uapi/linux/personality.h
> > @@ -22,6 +22,7 @@ enum {
> >  	WHOLE_SECONDS =		0x2000000,
> >  	STICKY_TIMEOUTS	=	0x4000000,
> >  	ADDR_LIMIT_3GB = 	0x8000000,
> > +	ADDR_LIMIT_47BIT = 	0x10000000,
> >  };
> 
> I wonder if ADDR_LIMIT_128T would be clearer?
> 

I don't follow, what does 128T represent?

> Have you looked at writing an update for the personality(2) man page? :)

I will write an update to the man page if this patch is approved!

> cheers

- Charlie