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Peter Anvin" , Klaus Kusche , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] x86/bugs: Qualify RETBLEED_INTEL_MSG Message-ID: <20251008102136.GAaOY7MBd4_VBPBNtG@fat_crate.local> References: <20251003171936.155391-1-david.kaplan@amd.com> <20251006131126.GBaOO__iUbQHNR6QhW@fat_crate.local> <20251006140442.GDaOPMemqB7SRJSHWL@fat_crate.local> <20251007182257.ywrqrrhgrtrviila@desk> <20251007221229.GAaOWQTadGWlZSeAo_@fat_crate.local> <20251007230821.5shpa3pusyzaohb2@desk> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: 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