From: Borislav Petkov <bp@alien8.de>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
"Kaplan, David" <David.Kaplan@amd.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>,
Klaus Kusche <klaus.kusche@computerix.info>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86/bugs: Qualify RETBLEED_INTEL_MSG
Date: Wed, 8 Oct 2025 12:21:36 +0200 [thread overview]
Message-ID: <20251008102136.GAaOY7MBd4_VBPBNtG@fat_crate.local> (raw)
In-Reply-To: <sb7p6quwxkn4w4etgsxlqd6fcsia4xobf73d3fnybxafxrmvwi@ajg5lkdxtnfy>
On Tue, Oct 07, 2025 at 05:14:29PM -0700, Josh Poimboeuf wrote:
> Isn't that what CONFIG_CPU_MITIGATIONS=n already does today?
I'd like =n to mean, code is not compiled in.
We do have some savings:
text data bss dec hex filename
136442490 9737118 36764336 182943944 ae780c8 vmlinux # CONFIG_CPU_MITIGATIONS is not set
138493310 10692818 37741668 186927796 b244ab4 vmlinux # CONFIG_CPU_MITIGATIONS=y
but look at bugs.o:
# CONFIG_CPU_MITIGATIONS is not set 599K arch/x86/kernel/cpu/bugs.o
# CONFIG_CPU_MITIGATIONS=y 625K arch/x86/kernel/cpu/bugs.o
and those unused 600K still go into vmlinux:
$ readelf -W -s vmlinux | grep cpu_show_
38058: ffffffff81869d20 27 FUNC LOCAL DEFAULT 1 cpu_show_not_affected
91642: ffffffff81284980 70 FUNC GLOBAL DEFAULT 1 cpu_show_vmscape
92944: ffffffff812840f0 68 FUNC GLOBAL DEFAULT 1 cpu_show_spectre_v1
93449: ffffffff812847e0 70 FUNC GLOBAL DEFAULT 1 cpu_show_gds
96967: ffffffff81869d20 27 FUNC WEAK DEFAULT 1 cpu_show_ghostwrite
99329: ffffffff812843b0 70 FUNC GLOBAL DEFAULT 1 cpu_show_spec_store_bypass
102119: ffffffff81284830 70 FUNC GLOBAL DEFAULT 1 cpu_show_reg_file_data_sampling
102618: ffffffff812845b0 56 FUNC GLOBAL DEFAULT 1 cpu_show_itlb_multihit
102660: ffffffff81284880 85 FUNC GLOBAL DEFAULT 1 cpu_show_old_microcode
103154: ffffffff812848e0 70 FUNC GLOBAL DEFAULT 1 cpu_show_indirect_target_selection
103474: ffffffff81284460 164 FUNC GLOBAL DEFAULT 1 cpu_show_mds
103673: ffffffff81284510 153 FUNC GLOBAL DEFAULT 1 cpu_show_tsx_async_abort
106613: ffffffff81284930 70 FUNC GLOBAL DEFAULT 1 cpu_show_tsa
109692: ffffffff81284400 92 FUNC GLOBAL DEFAULT 1 cpu_show_l1tf
111021: ffffffff81284640 150 FUNC GLOBAL DEFAULT 1 cpu_show_mmio_stale_data
111165: ffffffff812845f0 70 FUNC GLOBAL DEFAULT 1 cpu_show_srbds
112332: ffffffff81284090 83 FUNC GLOBAL DEFAULT 1 cpu_show_meltdown
114213: ffffffff812846e0 174 FUNC GLOBAL DEFAULT 1 cpu_show_retbleed
114312: ffffffff81284790 70 FUNC GLOBAL DEFAULT 1 cpu_show_spec_rstack_overflow
118586: ffffffff81284140 619 FUNC GLOBAL DEFAULT 1 cpu_show_spectre_v2
$ readelf -W -s vmlinux | grep _parse_cmdline
2575: ffffffff897a0050 27 FUNC LOCAL DEFAULT 18 nospectre_v2_parse_cmdline
2578: ffffffff897a0070 27 FUNC LOCAL DEFAULT 18 nossb_parse_cmdline
2587: ffffffff897a0110 37 FUNC LOCAL DEFAULT 18 its_parse_cmdline
2591: ffffffff897a01d0 138 FUNC LOCAL DEFAULT 18 tsx_async_abort_parse_cmdline
2594: ffffffff897a0260 138 FUNC LOCAL DEFAULT 18 mmio_stale_data_parse_cmdline
2597: ffffffff897a02f0 97 FUNC LOCAL DEFAULT 18 rfds_parse_cmdline
2599: ffffffff897a0360 56 FUNC LOCAL DEFAULT 18 srbds_parse_cmdline
2601: ffffffff897a03a0 38 FUNC LOCAL DEFAULT 18 l1d_flush_parse_cmdline
2603: ffffffff897a03d0 96 FUNC LOCAL DEFAULT 18 gds_parse_cmdline
2604: ffffffff897a0430 166 FUNC LOCAL DEFAULT 18 tsa_parse_cmdline
2606: ffffffff897a04e0 268 FUNC LOCAL DEFAULT 18 spectre_v2_user_parse_cmdline
2608: ffffffff897a05f0 487 FUNC LOCAL DEFAULT 18 spectre_v2_parse_cmdline
2609: ffffffff897a07e0 131 FUNC LOCAL DEFAULT 18 spectre_bhi_parse_cmdline
2611: ffffffff897a0870 206 FUNC LOCAL DEFAULT 18 ssb_parse_cmdline
2613: ffffffff897a0a30 200 FUNC LOCAL DEFAULT 18 srso_parse_cmdline
2615: ffffffff897a0b00 178 FUNC LOCAL DEFAULT 18 vmscape_parse_cmdline
2617: ffffffff897a0bc0 344 FUNC LOCAL DEFAULT 18 retbleed_parse_cmdline
and so on...
So I'd like to try to see whether completely axing it off in the =n case
without incurring a lot of ugly ifdeffery, would work.
> Then one only needs to grep their .config file for UGLY to understand
> why their disassembly is so inscrutable ;-)
Not sure about UGLY but if you can come up with a name that says "has impact
on the resulting code and when you have them enabled, you have weird asm
constructs all over the place", sure, why not.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2025-10-08 10:21 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-03 17:19 David Kaplan
2025-10-06 13:11 ` Borislav Petkov
2025-10-06 13:58 ` Kaplan, David
2025-10-06 14:04 ` Borislav Petkov
2025-10-07 18:22 ` Pawan Gupta
2025-10-07 22:12 ` Borislav Petkov
2025-10-07 23:08 ` Pawan Gupta
2025-10-08 0:14 ` Josh Poimboeuf
2025-10-08 10:21 ` Borislav Petkov [this message]
2025-10-09 1:07 ` Josh Poimboeuf
2025-10-09 10:19 ` Borislav Petkov
2025-10-09 6:04 ` Pawan Gupta
2025-10-09 10:15 ` Borislav Petkov
2025-10-09 17:13 ` Pawan Gupta
2025-10-09 18:13 ` Kaplan, David
2025-10-09 23:14 ` Borislav Petkov
2025-10-14 10:50 ` David Laight
2025-11-02 20:11 ` Borislav Petkov
2025-10-09 5:33 ` Pawan Gupta
2025-10-10 1:10 ` Josh Poimboeuf
2025-10-10 18:47 ` Pawan Gupta
2025-10-10 19:19 ` Josh Poimboeuf
2025-10-10 19:24 ` Pawan Gupta
2025-10-10 19:27 ` Kaplan, David
2025-10-10 20:47 ` Josh Poimboeuf
2025-10-10 21:13 ` Kaplan, David
2025-10-11 1:20 ` Josh Poimboeuf
2025-10-21 10:35 ` [tip: x86/urgent] " tip-bot2 for David Kaplan
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