netdev - 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: <02c00acd-9518-4371-be2c-eb63e5d11d9c@kernel.org>
Date: Thu, 5 Jun 2025 16:27:03 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>, x86@...nel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org,
 linux-arch@...r.kernel.org, netdev@...r.kernel.org
Cc: 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>
Subject: Large modules with 6.15 [was: [PATCH v4 6/6] percpu/x86: Enable
 strict percpu checks via named AS qualifiers]

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?

FTR downstream report:
https://bugzilla.suse.com/show_bug.cgi?id=1244135

thanks,
-- 
js
suse labs