Messages in this thread | | | Date | Wed, 11 May 2022 23:43:30 +0000 | Subject | [PATCH 0/2] x86/crash: Fix double list_add nmi_shootdown bug | From | Sean Christopherson <> |
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Fix a double list_add() bug found and debugged by Guilherme, who did all the hard work. nmi_shootdown_cpus() doesn't play nice with being called more than once. With the "right" kexec/kdump configuration, emergency_vmx_disable_all() can be reached after kdump_nmi_shootdown_cpus() (the two users of nmi_shootdown_cpus()).
My solution is to turn the emergency_vmx_disable_all() shootdown into a nop of sorts, and move the disabling of virtualization into the core crash_nmi_callback() handler. The only thing emergency_vmx_disable_all() cares about is disabling VMX/SVM (obviously), and since I can't envision a use case for an NMI shootdown that doesn't want to disable virtualization, doing that in the core handler means emergency_vmx_disable_all() only needs to ensure _a_ shootdown occurs, it doesn't care when that shootdown happened or what callback was run.
This obviously punts on making nmi_shootdown_cpus() truly multi-caller friendly, but notifier chains tend to be messy, and it's not obvious to me what would be the desired/correct behavior for a true multi-shootdown use case.
Patch 2 is a related bug fix found while exploring ideas for patch 1.
Sean Christopherson (2): x86/crash: Disable virt in core NMI crash handler to avoid double list_add x86/reboot: Disable virtualization in an emergency if SVM is supported
arch/x86/include/asm/reboot.h | 1 + arch/x86/kernel/crash.c | 16 +-------- arch/x86/kernel/reboot.c | 64 +++++++++++++++++++++++++++-------- 3 files changed, 51 insertions(+), 30 deletions(-)
base-commit: feb9c5e19e913b53cb536a7aa7c9f20107bb51ec -- 2.36.0.512.ge40c2bad7a-goog
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