netdev - 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: <8ea2aefc-2847-433e-b56e-5caad49e54f2@kernel.org>
Date: Thu, 5 Jun 2025 16:32:44 +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>,
 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]

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

-- 
js
suse labs