On Sun, Oct 22, 2017 at 05:16:29AM -0700, tip-bot for Borislav Petkov wrote: > +static void __fix_erratum_688(void *info) > +{ > +#define MSR_AMD64_IC_CFG 0xC0011021 > + > + msr_set_bit(MSR_AMD64_IC_CFG, 3); > + msr_set_bit(MSR_AMD64_IC_CFG, 14); I realize this is an erratum work around, but would it be too much to ask for a small comment explaining the magic values? > +} > + > +/* Apply erratum 688 fix so machines without a BIOS fix work. */ > +static __init void fix_erratum_688(void) > +{ > + struct pci_dev *F4; > + u32 val; > + > + if (boot_cpu_data.x86 != 0x14) > + return; > + > + if (!amd_northbridges.num) > + return; > + > + F4 = node_to_amd_nb(0)->link; > + if (!F4) > + return; > + > + if (pci_read_config_dword(F4, 0x164, &val)) > + return; > + > + if (val & BIT(2)) > + return; > + > + on_each_cpu(__fix_erratum_688, NULL, 0); > + > + pr_info("x86/cpu/AMD: CPU erratum 688 worked around\n"); Except for all CPUs that were not online at this point in time... So suppose I boot with a limited number of CPUs and then later bring up the rest, bad things happen.