forked from Minki/linux
151e0c7de6
Add disable_cpu_apicid kernel parameter. To use this kernel parameter, specify an initial APIC ID of the corresponding CPU you want to disable. This is mostly used for the kdump 2nd kernel to disable BSP to wake up multiple CPUs without causing system reset or hang due to sending INIT from AP to BSP. Kdump users first figure out initial APIC ID of the BSP, CPU0 in the 1st kernel, for example from /proc/cpuinfo and then set up this kernel parameter for the 2nd kernel using the obtained APIC ID. However, doing this procedure at each boot time manually is awkward, which should be automatically done by user-land service scripts, for example, kexec-tools on fedora/RHEL distributions. This design is more flexible than disabling BSP in kernel boot time automatically in that in kernel boot time we have no choice but referring to ACPI/MP table to obtain initial APIC ID for BSP, meaning that the method is not applicable to the systems without such BIOS tables. One assumption behind this design is that users get initial APIC ID of the BSP in still healthy state and so BSP is uniquely kept in CPU0. Thus, through the kernel parameter, only one initial APIC ID can be specified. In a comparison with disabled_cpu_apicid, we use read_apic_id(), not boot_cpu_physical_apicid, because on some platforms, the variable is modified to the apicid reported as BSP through MP table and this function is executed with the temporarily modified boot_cpu_physical_apicid. As a result, disabled_cpu_apicid kernel parameter doesn't work well for apicids of APs. Fixing the wrong handling of boot_cpu_physical_apicid requires some reviews and tests beyond some platforms and it could take some time. The fix here is a kind of workaround to focus on the main topic of this patch. Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> Link: http://lkml.kernel.org/r/20140115064458.1545.38775.stgit@localhost6.localdomain6 Signed-off-by: H. Peter Anvin <hpa@zytor.com> |
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