BTW, I'm basically moving forward assuming that we're going to apply this patch in _some_ form. I'm going to make some changes, but I'll discuss them in this thread to make sure we're all on the same page first. On 1/24/23 17:28, Eric Biggers wrote: > +Affected CPUs > +------------- > + > +This vulnerability affects Intel Core family processors based on the Ice Lake > +and later microarchitectures, and Intel Atom family processors based on the > +Gracemont and later microarchitectures. For more information, see Intel's > +documentation [1]_. I had a hard time following the docs in this area. But I'm not sure this statement is correct. The docs actually say: For Intel® Core™ family processors based on microarchitectures before Ice Lake and Intel Atom® family processors based on microarchitectures before Gracemont that do not enumerate IA32_UARCH_MISC_CTL, developers may assume that the instructions listed here operate as if DOITM is enabled. A processor needs to be before "Ice Lake" and friends *AND* not enumerate IA32_UARCH_MISC_CTL to be unaffected. There's also another tweak that's needed because: Processors that do not enumerate IA32_ARCH_CAPABILITIES[DOITM] when the latest microcode is applied do not need to set IA32_UARCH_MISC_CTL [DOITM] in order to have the behavior described in this document... First, we need to mention the "latest microcode" thing in the kernel docs. I also _think_ the whole "microarchitectures before" stuff is rather irrelevant and we can simplify this down to: This vulnerability affects all Intel processors that support MSR_IA32_ARCH_CAPABILITIES and set MSR_IA32_ARCH_CAPABILITIES[DOITM] when the latest microcode is applied. Which reminds me. This: > +void update_doitm_msr(void) > +{ > + u64 msr; > + > + if (doitm_off) > + return; > + > + rdmsrl(MSR_IA32_UARCH_MISC_CTL, msr); > + wrmsrl(MSR_IA32_UARCH_MISC_CTL, msr | UARCH_MISC_DOITM); > +} should probably be: void update_doitm_msr(void) { u64 msr; /* * All processors that enumerate support for DOIT * are affected *and* have the mitigation available. */ if (!boot_cpu_has_bug(X86_BUG_DODT)) return; rdmsrl(MSR_IA32_UARCH_MISC_CTL, msr); if (doitm_off) msr &= ~UARCH_MISC_DOITM; else msr |= UARCH_MISC_DOITM; wrmsrl(MSR_IA32_UARCH_MISC_CTL, msr); } in case the CPU isn't actually coming out of reset, like if kexec() left DOITM=1.