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Tue, 10 Nov 2026 02:58:06 +0000 Message-ID: <35c49d1a-4447-48de-9741-dd6200dfe8a8@intel.com> Date: Mon, 9 Nov 2026 18:58:03 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/9] stop_machine: Add NMI-based execution path To: Borislav Petkov CC: , , , , , , References: <20261104182322.578066-1-chang.seok.bae@intel.com> <20261104182322.578066-3-chang.seok.bae@intel.com> <20261110024646.GGavKFllskPQiLrNOK@fat_crate.local> Content-Language: en-US From: "Chang S. 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Bae wrote: >> +/* >> + * Instrumentation may trigger nested exceptions such as #INT3, #DB, >> + * or #PF. IRET from those would re-enable NMIs, which opposes the goal >> + * of this NMI stop-machine facility. >> + */ >> +bool noinstr stop_machine_nmi_handler(void) > > stop_machine_nmi() > >> +{ >> + struct multi_stop_data *msdata = raw_cpu_read(nmi_stop.data); >> + unsigned int cpu = raw_smp_processor_id(); >> + int ret; >> + >> + if (!msdata || !arch_test_and_clear_bit(cpu, cpumask_bits(msdata->nmi_cpus))) >> + return false; >> + >> + /* >> + * The indirect call to @nmisafe_fn() is indistinguishable at >> + * post-compilation. Temporarily enabling instrumentation avoids >> + * objtool false positives. >> + */ >> + instrumentation_begin(); >> + ret = msdata->nmisafe_fn(msdata->data); >> + instrumentation_end(); > > This is just silly. We should fix objtool here. Here is your previous thought: This one would be hard to fix because that's the err = msdata->fn(msdata->data); function pointer which objtool can't see through. https://lore.kernel.org/lkml/20260127144947.GKaXjQi8R9cE17WYKM@fat_crate.local/