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

Charlie Jenkins posted 2 patches 4 months, 1 week ago
[PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Charlie Jenkins 4 months, 1 week ago 
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 <charlie@rivosinc.com>
---
 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,
 };
 
 /*
diff --git a/mm/mmap.c b/mm/mmap.c
index d0dfc85b209b..a5c7544853e5 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1766,6 +1766,9 @@ unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
 {
 	unsigned long addr;
 
+	if (current->personality & ADDR_LIMIT_47BIT)
+		info->high_limit = MIN(info->high_limit, BIT(47) - 1);
+
 	if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
 		addr = unmapped_area_topdown(info);
 	else

-- 
2.45.0
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Michael Ellerman 4 months, 1 week ago 
Charlie Jenkins <charlie@rivosinc.com> 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 <charlie@rivosinc.com>
> ---
>  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?

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

cheers
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Charlie Jenkins 4 months, 1 week ago 
On Fri, Sep 06, 2024 at 04:59:40PM +1000, Michael Ellerman wrote:
> Charlie Jenkins <charlie@rivosinc.com> 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 <charlie@rivosinc.com>
> > ---
> >  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
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Michael Ellerman 4 months ago 
Charlie Jenkins <charlie@rivosinc.com> writes:
> On Fri, Sep 06, 2024 at 04:59:40PM +1000, Michael Ellerman wrote:
>> Charlie Jenkins <charlie@rivosinc.com> 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 <charlie@rivosinc.com>
>> > ---
>> >  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?

Sorry, as Christophe explained it's 128 Terabytes, which is the actual
value of the address limit.

I think expressing it as the address value is probably more widely
understood, and would also match ADDR_LIMIT_3GB.

>> 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!

Yeah fair enough.

My (poorly expressed) point was that trying to describe the flag for the
man page might highlight that using the 47BIT name requires more
explanation.

cheers
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Christophe Leroy 4 months ago 
>>> 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?
> 

128T is 128 Terabytes, that's the maximum size achievable with a 47BIT 
address, that naming would be more consistant with the ADDR_LIMIT_3GB 
just above that means a 3 Gigabytes limit.

Christophe
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Geert Uytterhoeven 4 months ago 
Hi Christophe,

On Tue, Sep 10, 2024 at 11:21 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
> >>> 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?
>
> 128T is 128 Terabytes, that's the maximum size achievable with a 47BIT
> address, that naming would be more consistant with the ADDR_LIMIT_3GB
> just above that means a 3 Gigabytes limit.

Hence ADDR_LIMIT_128TB?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Michael Ellerman 4 months ago 
Geert Uytterhoeven <geert@linux-m68k.org> writes:
> Hi Christophe,
>
> On Tue, Sep 10, 2024 at 11:21 AM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>> >>> 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?
>>
>> 128T is 128 Terabytes, that's the maximum size achievable with a 47BIT
>> address, that naming would be more consistant with the ADDR_LIMIT_3GB
>> just above that means a 3 Gigabytes limit.
>
> Hence ADDR_LIMIT_128TB?

Yes it should be 128TB. Typo by me.

cheers
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Charlie Jenkins 4 months ago 
On Wed, Sep 11, 2024 at 11:38:55PM +1000, Michael Ellerman wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> writes:
> > Hi Christophe,
> >
> > On Tue, Sep 10, 2024 at 11:21 AM Christophe Leroy
> > <christophe.leroy@csgroup.eu> wrote:
> >> >>> 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?
> >>
> >> 128T is 128 Terabytes, that's the maximum size achievable with a 47BIT
> >> address, that naming would be more consistant with the ADDR_LIMIT_3GB
> >> just above that means a 3 Gigabytes limit.
> >
> > Hence ADDR_LIMIT_128TB?
> 
> Yes it should be 128TB. Typo by me.
> 
> cheers

47BIT was selected because the usecase for this flag is for applications
that want to store data in the upper bits of a virtual address space. In
this case, how large the virtual address space is irrelevant, and only
the number of bits that are being used, and hence the number of bits
that are free.

- Charlie
Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Posted by Michael Ellerman 3 months, 3 weeks ago 
Charlie Jenkins <charlie@rivosinc.com> writes:
> On Wed, Sep 11, 2024 at 11:38:55PM +1000, Michael Ellerman wrote:
>> Geert Uytterhoeven <geert@linux-m68k.org> writes:
>> > Hi Christophe,
>> >
>> > On Tue, Sep 10, 2024 at 11:21 AM Christophe Leroy
>> > <christophe.leroy@csgroup.eu> wrote:
>> >> >>> 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?
>> >>
>> >> 128T is 128 Terabytes, that's the maximum size achievable with a 47BIT
>> >> address, that naming would be more consistant with the ADDR_LIMIT_3GB
>> >> just above that means a 3 Gigabytes limit.
>> >
>> > Hence ADDR_LIMIT_128TB?
>> 
>> Yes it should be 128TB. Typo by me.
>
> 47BIT was selected because the usecase for this flag is for applications
> that want to store data in the upper bits of a virtual address space. In
> this case, how large the virtual address space is irrelevant, and only
> the number of bits that are being used, and hence the number of bits
> that are free.

Yeah I understand that's how you came to the problem.

But for the user API I think using the size of the address space is
clearer, easier to explain, and matches the existing ADDR_LIMIT_3GB.

cheers

Patchew 2.1-devel-b67e4c2

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