[coreboot] Broadwell-DE hang in coreboot: mp_init.c

[mark pleso]

Has anyone else seen a hang during coreboot booting on a Broadwell-DE?  The issue appears to be in mp_init.c, in the function smm_do_relocation().  This is coreboot 4.7, but I think the issue exists in 4.6 as well.
Enabling the printk will stop the hang. Or, just adding a wbinvd() instruction will stop the hang, and things proceed normally.  Code is below.
Any help would be appreciated.
btw - This not a commercial motherboard.
coreboot/src/cpu/x86/mp_init.cstatic void asmlinkage smm_do_relocation(void *arg)
{        const struct smm_module_params *p;        const struct smm_runtime *runtime;        int cpu;        uintptr_t curr_smbase;        uintptr_t perm_smbase;
        p = arg;        runtime = p->runtime;        cpu = p->cpu;        curr_smbase = runtime->smbase;
        if (cpu >= CONFIG_MAX_CPUS) {                printk(BIOS_CRIT,                       "Invalid CPU number assigned in SMM stub: %d\n", cpu);                return;        }
        /*         * The permanent handler runs with all cpus concurrently. Precalculate         * the location of the new SMBASE. If using SMM modules then this         * calculation needs to match that of the module loader.         */        perm_smbase = mp_state.perm_smbase;        perm_smbase -= cpu * runtime->save_state_size;
        printk(BIOS_DEBUG, "New SMBASE 0x%08lx\n", perm_smbase);
        /* write cache to DRAM before calling relocation handler */ /* will stop hang */        wbinvd();  /* <<=== OR NEW INSTRUCTION w/o printk STOPS HANG */
        /* Setup code checks this callback for validity. */        mp_state.ops.relocation_handler(cpu, curr_smbase, perm_smbase);}
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.coreboot.org/pipermail/coreboot/attachments/20180226/7149c6bb/attachment.html>