On Tue, Dec 18, 2012 at 1:50 AM, Zhang, Lin-Bao (Linux Kernel R&D) <[email protected]> wrote: > Hi Suresh and other guys , > > In 3.4.4/3.6.6 ,I found a x2apic issue . if I am wrong , sorry first > , and welcome your correction . thanks for your forwarding other maintainers. > I am testing a server , its BIOS is like this: > a) If BIOS think the system is of x2apic , it will set x2apic enablement bit > in MSR and create x2apic ACPI tables and pass control to OS with x2apic mode
kernel will check if DMAR table is right or not, if intr-remapping could be enabled, kernel will stay with x2apic. if intr-remapping can not be enabled (bad dmar table), kernel will switch back to xapic mode, but if BSP's X2APIC is bigger than 255, then you will get kernel panic. > b) If BIOS feel the system doesn't meet x2apic conditions , it will not set > x2apic enablement bit in MSR ,and pass control to OS with xapic mode. kernel will check if cpuid support x2apic, if it supports x2apic, it will check if DMAR/intr-remapping could be enabled, if so kernel will switch to x2apic. otherwise it will stay with xapic. So you need to make cpuid show does not support x2apic --- check with intel they have way to do that. or you can pass "nox2apic" in boot command line. Yinghai -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
