On 11.02.2022 12:19, Roger Pau Monné wrote: > On Fri, Feb 11, 2022 at 11:50:46AM +0100, Jan Beulich wrote: >> On 11.02.2022 11:47, Roger Pau Monné wrote: >>> On Fri, Feb 11, 2022 at 11:32:45AM +0100, Jan Beulich wrote: >>>> On 11.02.2022 10:02, Roger Pau Monné wrote: >>>>> On Fri, Feb 11, 2022 at 08:23:27AM +0100, Norbert Manthey wrote: >>>>>> When re-identifying CPU data, we might use uninitialized data when >>>>>> checking for the cache line property to adapt the cache >>>>>> alignment. The data that depends on this uninitialized read is >>>>>> currently not forwarded. >>>>>> >>>>>> To avoid problems in the future, initialize the data cpuinfo >>>>>> structure before re-identifying the CPU again. >>>>>> >>>>>> The trace to hit the uninitialized read reported by Coverity is: >>>>>> >>>>>> bool recheck_cpu_features(unsigned int cpu) >>>>>> ... >>>>>> struct cpuinfo_x86 c; >>>>>> ... >>>>>> identify_cpu(&c); >>>>>> >>>>>> void identify_cpu(struct cpuinfo_x86 *c) >>>>>> ... >>>>>> generic_identify(c) >>>>>> >>>>>> static void generic_identify(struct cpuinfo_x86 *c) >>>>>> ... >>>>> >>>>> Would it be more appropriate for generic_identify to also set >>>>> x86_cache_alignment like it's done in early_cpu_init? >>>>> >>>>> generic_identify already re-fetches a bunch of stuff that's also >>>>> set by early_cpu_init for the BSP. >>>> >>>> This would be an option, but how sure are you that there isn't >>>> (going to be) another field with similar properties? We better >>>> wouldn't require _everything_ to be re-filled in generic_identify(). >>> >>> So you think generic_identify should call into early_cpu_init, or even >>> split the cpuinfo_x86 filling done in early_cpu_init into a non-init >>> function that could be called by both generic_identify and >>> early_cpu_init? >> >> No, I think it is quite fine for this to be a two-step process. > > But it's not a two step process for all CPUs. It's a two step process > for the BSP, that will get it's cpuinfo filled by early_cpu_init > first, and then by identify_cpu. OTHO APs will only get the > information filled by identify_cpu. > > Maybe APs don't care about having x86_cache_alignment correctly set?
They do care, and the field also isn't left uninitialized. See initialize_cpu_data(). Like in many other places we assume full symmetry among processors here. Jan
