Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support"
On 01/10/23 at 10:24am, Baoquan He wrote:
> On 01/09/23 at 10:59pm, Thomas Gleixner wrote:
> > On Tue, Dec 20 2022 at 13:34, Baoquan He wrote:
> > > This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92.
> > >
> > > On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal
> > > kernel's cmdline, and triggering crash to jump to kdump kernel, kdump
> > > kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic:
> > > Implement IPI shorthands support") can fix it.
> >
> > Is there any output on the early console or hangs it silently?
> >
> > If the latter, can you attach GDB to the guest and figure out where it
> > is stuck?
>
> No any output on the ealry console. I will try gdb debugging. Thanks.
I rebase to the latest upstream kernel and tested, the stable kdump
kernel hang disappear. Seems I need do another round of bisect to see
on which commit it's made to fix that. Will update if any progress.
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Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support"
On 01/09/23 at 10:59pm, Thomas Gleixner wrote:
> On Tue, Dec 20 2022 at 13:34, Baoquan He wrote:
> > This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92.
> >
> > On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal
> > kernel's cmdline, and triggering crash to jump to kdump kernel, kdump
> > kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic:
> > Implement IPI shorthands support") can fix it.
>
> Is there any output on the early console or hangs it silently?
>
> If the latter, can you attach GDB to the guest and figure out where it
> is stuck?
No any output on the ealry console. I will try gdb debugging. Thanks.
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Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support"
On Tue, Dec 20 2022 at 13:34, Baoquan He wrote:
> This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92.
>
> On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal
> kernel's cmdline, and triggering crash to jump to kdump kernel, kdump
> kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic:
> Implement IPI shorthands support") can fix it.
Is there any output on the early console or hangs it silently?
If the latter, can you attach GDB to the guest and figure out where it
is stuck?
Thanks,
tglx
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Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support"
* Baoquan He (b...@redhat.com) wrote:
> On 12/20/22 at 12:38pm, Peter Zijlstra wrote:
> > On Tue, Dec 20, 2022 at 01:34:58PM +0800, Baoquan He wrote:
> > > This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92.
> > >
> > > On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal
> > > kernel's cmdline, and triggering crash to jump to kdump kernel, kdump
> > > kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic:
> > > Implement IPI shorthands support") can fix it.
> > >
> > > The problem will disappear if removing 'nr_cpus=2' from normal kerne's
> > > cmdline.
> >
> > And the root cause for this is... ? Does the kvm x2apic emulation
> > somehow get upset when we shorthand CPUs that haven't been initialized?
>
> Thanks for checking.
>
> I haven't figure out the root cause. I haven't read the apic code for
> long time, and not familiar with the kvm code. So raise the issue to
> upstream.
>
> I can do testing if any suggestion.
>
> Add our virt dev Dr. David Alan Gilbert to CC.
Hmm I don't know that code well enough; cc'ing Paolo and Maxim.
Dave
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
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Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support"
On 12/20/22 at 12:38pm, Peter Zijlstra wrote:
> On Tue, Dec 20, 2022 at 01:34:58PM +0800, Baoquan He wrote:
> > This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92.
> >
> > On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal
> > kernel's cmdline, and triggering crash to jump to kdump kernel, kdump
> > kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic:
> > Implement IPI shorthands support") can fix it.
> >
> > The problem will disappear if removing 'nr_cpus=2' from normal kerne's
> > cmdline.
>
> And the root cause for this is... ? Does the kvm x2apic emulation
> somehow get upset when we shorthand CPUs that haven't been initialized?
Thanks for checking.
I haven't figure out the root cause. I haven't read the apic code for
long time, and not familiar with the kvm code. So raise the issue to
upstream.
I can do testing if any suggestion.
Add our virt dev Dr. David Alan Gilbert to CC.
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Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support"
On Tue, Dec 20, 2022 at 01:34:58PM +0800, Baoquan He wrote:
> This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92.
>
> On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal
> kernel's cmdline, and triggering crash to jump to kdump kernel, kdump
> kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic:
> Implement IPI shorthands support") can fix it.
>
> The problem will disappear if removing 'nr_cpus=2' from normal kerne's
> cmdline.
And the root cause for this is... ? Does the kvm x2apic emulation
somehow get upset when we shorthand CPUs that haven't been initialized?
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