Messages in this thread | | | Date | Thu, 23 Feb 2023 11:14:00 +0800 | Subject | Re: [RFC PATCH v4] x86/kdump: terminate watchdog NMI interrupt to avoid kdump crashes | From | Zeng Heng <> |
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在 2023/2/23 10:29, Zeng Heng 写道: > > 在 2023/2/23 2:39, Eric W. Biederman 写道: >> Peter Zijlstra <peterz@infradead.org> writes: >> >>> On Fri, Feb 17, 2023 at 08:06:04PM +0800, Zeng Heng wrote: >>>> If the cpu panics within the NMI interrupt context, there could be >>>> unhandled NMI interrupts in the background which are blocked by >>>> processor >>>> until next IRET instruction executes. Since that, it prevents nested >>>> NMI handler execution. >>>> >>>> In case of IRET execution during kdump reboot and no proper NMIs >>>> handler >>>> registered at that point (such as during EFI loader) >> EFI loader? kexec on panic is supposed to be kernel to kernel. >> If someone is getting EFI involved that is a bug. > > In kdump path, kexec would start purgatory to verify the secondary > kernel by > > sha256. If verify passed, it would turn the control to EFI loader, and > call the second > > kernel to capture the environment as vmcore file. > > As the mail said, if panic appears within NMI context, we never exit > from that until > > EFI loader handles page fault exception and executes IRET instruction > when exit > > from PF. At this moment, processor would allow the blocked NMI > interrupt raise. > > >>> This kills all of perf, including but not limited to the hardware >>> watchdog. However, it does nothing to external NMI sources like the NMI >>> button found on some HP machines. >>> >>> Still I suppose it is sufficient for the normal case. >> I can't think of one why we don't just leave >> NMIs deliberately disabled > Inative_machine_crash_shutdown() has called lapic_shutdown() to disable any kind of
irq, but EFI loader assumes there is no any residual NMIs in the background.
Here is the first version for this issue:
https://lore.kernel.org/all/20230110102745.2514694-1-zengheng4@huawei.com/
Zeng Heng
> >> until the crash recover kernel figured out how to enable them safely. >> >
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