Messages in this thread | | | Date | Wed, 30 Nov 2022 23:36:46 +0000 | Subject | [PATCH v4 0/4] x86/crash: Fix double NMI shootdown bug | From | Sean Christopherson <> |
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Fix a double NMI shootdown bug found and debugged by Guilherme, who did all the hard work. NMI shootdown is a one-time thing; the handler leaves NMIs blocked and enters halt. At best, a second (or third...) shootdown is an expensive nop, at worst it can hang the kernel and prevent kexec'ing into a new kernel, e.g. prior to the hardening of register_nmi_handler(), a double shootdown resulted in a double list_add(), which is fatal when running with CONFIG_BUG_ON_DATA_CORRUPTION=y.
With the "right" kexec/kdump configuration, emergency_vmx_disable_all() can be reached after kdump_nmi_shootdown_cpus() (currently the only two users of nmi_shootdown_cpus()).
To fix, move the disabling of virtualization into crash_nmi_callback(), remove emergency_vmx_disable_all()'s callback, and do a shootdown for emergency_vmx_disable_all() if and only if a shootdown hasn't yet occurred. 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 may have run.
Patches 2-4 bring SVM on par with VMX.
v4: - Set GIF=1 prior to disabling SVM. [Andrew, Tom] - Name new helper cpu_emergency_disable_virtualization() instead of cpu_crash_disable_virtualization(). - Add patch to handle SVM in the stop/reboot case. - Drop patch to fold __cpu_emergency_vmxoff() into cpu_emergency_vmxoff(), will be sent as part of a larger cleanup.
v3: - https://lore.kernel.org/all/20221114233441.3895891-1-seanjc@google.com - Re-collect Guilherme's Tested-by. - Tweak comment in patch 1 to reference STGI instead of CLGI. - Celebrate this series' half-birthday.
v2: - Use a NULL handler and crash_ipi_issued instead of a magic nop handler. [tglx] - Add comments to call out that modifying the existing handler once the NMI is sent may cause explosions. - Add a patch to cleanup cpu_emergency_vmxoff(). - https://lore.kernel.org/all/20220518001647.1291448-1-seanjc@google.com
v1: https://lore.kernel.org/all/20220511234332.3654455-1-seanjc@google.com
Sean Christopherson (4): x86/crash: Disable virt in core NMI crash handler to avoid double shootdown x86/virt: Force GIF=1 prior to disabling SVM (for reboot flows) x86/reboot: Disable virtualization in an emergency if SVM is supported x86/reboot: Disable SVM, not just VMX, when stopping CPUs
arch/x86/include/asm/reboot.h | 2 + arch/x86/include/asm/virtext.h | 13 ++++- arch/x86/kernel/crash.c | 17 +------ arch/x86/kernel/reboot.c | 88 ++++++++++++++++++++++++---------- arch/x86/kernel/smp.c | 6 +-- 5 files changed, 82 insertions(+), 44 deletions(-)
base-commit: d800169041c0e035160c8b81f30d4b7e8f8ef777 -- 2.38.1.584.g0f3c55d4c2-goog
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