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SubjectRe: [PATCH v4 0/3] x86, apic, kexec: Add disable_cpu_apic kernel parameter
Hi,

I am reviewing this patchset, and found there's a cpu0 hotplug feature
posted by intel which we can borrow an idea from. In that implementation,
CPU0 is waken up by nmi not INIT to avoid the realmode bootstrap code
execution. I tried it by below patch which includes one line of change.

By console printing, I got the boot cpu is always 0(namely cpu=0),
however the apicid related to each processor keeps the same as in 1st
kernel. In my HP Z420 machine, the apicid for BSP is 0, so I just make a
test patch which depends on the fact that apicid for BSP is 0. Maybe
generally the apicid for BSP can't be guaranteed, then passing it from
1st kernel to 2nd kernel in cmdline is very helpful, just as you have
done for disable_cpu_apic.

On my HP z420, I add nr_cpus=4 in /etc/sysconfig/kdump, and then execute
below command, then 3 APs (1 boot cpu and 2 AP) can be waken up
correctly, but BSP failed because NMI received for unknown reason 21 on
CPU0. I think I need further check why BSP failed to wake up by nmi. But
3 processors are brought up successfully and kdump is successful too.

sudo taskset -c 1 sh -c "echo c >/proc/sysrq-trigger"

[ 0.296831] smpboot: Booting Node 0, Processors # 1
[ 0.302095]
*****************************************************cpu=1, apicid=0, wakeup_cpu_via_init_nmi
[ 0.311942] cpu=1, apicid=0, register_nmi_handlercpu=1, apicid=0, wakeup_secondary_cpu_via_nmi
[ 0.320826] Uhhuh. NMI received for unknown reason 21 on CPU 0.
[ 0.327129] Do you have a strange power saving mode enabled?
[ 0.333858] Dazed and confused, but trying to continue
[ 0.339290] cpu=1, apicid=0, wakeup_cpu_via_init_nmi
[ 2.409099] Uhhuh. NMI received for unknown reason 21 on CPU 0.
[ 2.415393] Do you have a strange power saving mode enabled?
[ 2.421142] Dazed and confused, but trying to continue
[ 5.379519] smpboot: CPU1: Not responding
[ 5.383692] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter.

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 6cacab6..e45fe5b 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -702,7 +702,7 @@ wakeup_cpu_via_init_nmi(int cpu, unsigned long
start_ip, int apicid,
/*
* Wake up AP by INIT, INIT, STARTUP sequence.
*/
- if (cpu)
+ if (cpu && apicid)
return wakeup_secondary_cpu_via_init(apicid, start_ip);

/*


On 10/23/13 at 12:01am, HATAYAMA Daisuke wrote:
> This patch set is to allow kdump 2nd kernel to wake up multiple CPUs
> even if 1st kernel crashs on some AP, a continueing work from:
>
> [PATCH v3 0/2] x86, apic, kdump: Disable BSP if boot cpu is AP
> https://lkml.org/lkml/2013/10/16/300.
>
> In this version, basic design has changed. Now users need to figure
> out initial APIC ID of BSP in the 1st kernel and configures kernel
> parameter for the 2nd kernel manually using disable_cpu_apic kernel
> parameter to be newly introduced in this patch set. This design is
> more flexible than the previous version in that we no longer have to
> rely on ACPI/MP table to get initial APIC ID of BSP.
>
> Sorry, this patch set have not include in-source documentation
> requested by Borislav Petkov yet, but I'll post it later separately,
> which would be better to focus on documentation reviewing.
>
> ChangeLog
>
> v3 => v4)
>
> - Rebased on top of v3.12-rc6
>
> - Basic design has been changed. Now users need to figure out initial
> APIC ID of BSP in the 1st kernel and configures kernel parameter for
> the 2nd kernel manually using disable_cpu_apic kernel parameter to
> be newly introduced in this patch set. This design is more flexible
> than the previous version in that we no longer have to rely on
> ACPI/MP table to get initial APIC ID of BSP.
>
> v2 => v3)
>
> - Change default value of boot_cpu_is_bsp to true.
>
> - Before executing rdmsr(MSR_IA32_APICBASE), check if the number of
> processor family is larger than or equal to 6 in order to avoid
> invalid opcode exception on processors where MSR_IA32_APICBASE is
> not supported.
>
> v1 => v2)
>
> - Rebased on top of v3.12-rc5.
>
> - Fix linking time error of boot_cpu_is_bsp_init() in case of
> CONFIG_LOCAL_APIC disabled by adding empty static inline function
> instead.
>
> - Fix missing feature check by means of cpu_has_apic macro in
> boot_cpu_is_bsp_init() before calling rdmsr_safe(MSR_IA32_APICBASE).
>
> NOTE: I've checked local apic-present case only; I don't have any
> x86 processor without local apic.
>
> - Add __init annotation to boot_cpu_is_bsp_init().
>
> Test
>
> - built with and without CONFIG_LOCAL_APIC
> - tested x86_64 in case of acpi and MP table
>
> ---
>
> HATAYAMA Daisuke (3):
> x86, apic: Don't count the CPU with BP flag from MP table as booting-up CPU
> x86, apic: Add disable_cpu_apicid kernel parameter
> Documentation, x86, apic, kexec: Add disable_cpu_apicid kernel parameter
>
>
> Documentation/kernel-parameters.txt | 9 +++++++++
> arch/x86/kernel/apic/apic.c | 29 +++++++++++++++++++++++++++++
> arch/x86/kernel/mpparse.c | 1 -
> 3 files changed, 38 insertions(+), 1 deletion(-)
>
> --
>
> Thanks.
> HATAYAMA, Daisuke
>
> _______________________________________________
> kexec mailing list
> kexec@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec


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