linux-kernel - Re: Large modules with 6.15 [was: [PATCH v4 6/6] percpu/x86: Enable strict percpu checks via named AS qualifiers]

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Message-ID: <CAADnVQ+ukqmyNJ7eT8Z=2GY5cGAt38VJtzOjEbH_3aKCUC5qLg@mail.gmail.com>
Date: Thu, 5 Jun 2025 09:17:19 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Uros Bizjak <ubizjak@...il.com>, X86 ML <x86@...nel.org>, linux-mm <linux-mm@...ck.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-bcachefs@...r.kernel.org, 
	linux-arch <linux-arch@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, 
	Nadav Amit <nadav.amit@...il.com>, Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, 
	Christoph Lameter <cl@...ux.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	"H. Peter Anvin" <hpa@...or.com>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>, 
	Peter Zijlstra <peterz@...radead.org>, Shung-Hsi Yu <shung-hsi.yu@...e.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	John Fastabend <john.fastabend@...il.com>, bpf <bpf@...r.kernel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>
Subject: Re: Large modules with 6.15 [was: [PATCH v4 6/6] percpu/x86: Enable
 strict percpu checks via named AS qualifiers]

On Thu, Jun 5, 2025 at 7:32 AM Jiri Slaby <jirislaby@...nel.org> wrote:
>
> Cc BPF people, just so you know.
>
> On 05. 06. 25, 16:27, Jiri Slaby wrote:
> > On 27. 01. 25, 17:05, Uros Bizjak wrote:
> >> This patch declares percpu variables in __seg_gs/__seg_fs named AS
> >> and keeps them named AS qualified until they are dereferenced with
> >> percpu accessor. This approach enables various compiler check
> >> for cross-namespace variable assignments.
> >>
> >> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> >> Acked-by: Nadav Amit <nadav.amit@...il.com>
> >> Cc: Dennis Zhou <dennis@...nel.org>
> >> Cc: Tejun Heo <tj@...nel.org>
> >> Cc: Christoph Lameter <cl@...ux.com>
> >> Cc: Thomas Gleixner <tglx@...utronix.de>
> >> Cc: Ingo Molnar <mingo@...nel.org>
> >> Cc: Borislav Petkov <bp@...en8.de>
> >> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> >> Cc: "H. Peter Anvin" <hpa@...or.com>
> >> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> >> Cc: Andy Lutomirski <luto@...nel.org>
> >> Cc: Brian Gerst <brgerst@...il.com>
> >> Cc: Peter Zijlstra <peterz@...radead.org>
> >> ---
> >>   arch/x86/include/asm/percpu.h | 15 ++++++++++++---
> >>   1 file changed, 12 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/
> >> percpu.h
> >> index 27f668660abe..474d648bca9a 100644
> >> --- a/arch/x86/include/asm/percpu.h
> >> +++ b/arch/x86/include/asm/percpu.h
> >> @@ -95,9 +95,18 @@
> >>   #endif /* CONFIG_SMP */
> >> -#define __my_cpu_type(var)    typeof(var) __percpu_seg_override
> >> -#define __my_cpu_ptr(ptr)    (__my_cpu_type(*(ptr))*)(__force
> >> uintptr_t)(ptr)
> >> -#define __my_cpu_var(var)    (*__my_cpu_ptr(&(var)))
> >> +#if defined(CONFIG_USE_X86_SEG_SUPPORT) && defined(USE_TYPEOF_UNQUAL)
> >> +# define __my_cpu_type(var)    typeof(var)
> >> +# define __my_cpu_ptr(ptr)    (ptr)
> >> +# define __my_cpu_var(var)    (var)
> >> +
> >> +# define __percpu_qual        __percpu_seg_override
> >> +#else
> >> +# define __my_cpu_type(var)    typeof(var) __percpu_seg_override
> >> +# define __my_cpu_ptr(ptr)    (__my_cpu_type(*(ptr))*)(__force
> >> uintptr_t)(ptr)
> >> +# define __my_cpu_var(var)    (*__my_cpu_ptr(&(var)))
> >> +#endif
> >> +
> >
> > Another issue with this is this causes all modules in 6.15 are 2-4 times
> > (compressed size) bigger:
> > $ ll /usr/lib/modules/*-[0-9]-default/kernel/drivers/atm/atmtcp.ko.zst
> >  > -rw-r--r--. 1 root root 10325 May 13 11:49 /usr/lib/modules/6.14.6-2-
> > default/kernel/drivers/atm/atmtcp.ko.zst
> >  > -rw-r--r--. 1 root root 39677 Jun  2 09:13 /usr/lib/modules/6.15.0-1-
> > default/kernel/drivers/atm/atmtcp.ko.zst
> >
> > It's due to larger .BTF section:
> > .BTF              PROGBITS         0000000000000000  [-00003080-]
> > [-       00000000000011a8-]  {+00003100+}
> > {+       0000000000012cf8+}  0000000000000000           0     0     1
> >
> > There are a lot of new BTF types defined in each module like:
> > +attribute_group STRUCT
> > +backing_dev_info STRUCT
> > +bdi_writeback STRUCT
> > +bin_attribute STRUCT
> > +bio_end_io_t TYPEDEF
> > +bio_list STRUCT
> > +bio_set STRUCT
> > +bio STRUCT
> > +bio_vec STRUCT
> >
> > Reverting this gives me back to normal sizes.
> >
> > Any ideas?

Try newer pahole ?
It was fixed by:
https://lore.kernel.org/bpf/20250429161042.2069678-1-alan.maguire@oracle.com/