Sean Christopherson 26044aff37 x86/crash: Disable virt in core NMI crash handler to avoid double shootdown ... Disable virtualization in crash_nmi_callback() and rework the emergency_vmx_disable_all() path to do an NMI shootdown if and only if a shootdown has not already occurred. NMI crash shootdown fundamentally can't support multiple invocations as responding CPUs are deliberately put into halt state without unblocking NMIs. But, the emergency reboot path doesn't have any work of its own, it simply cares about disabling virtualization, i.e. so long as a shootdown occurred, emergency reboot doesn't care who initiated the shootdown, or when. If "crash_kexec_post_notifiers" is specified on the kernel command line, panic() will invoke crash_smp_send_stop() and result in a second call to nmi_shootdown_cpus() during native_machine_emergency_restart(). Invoke the callback _before_ disabling virtualization, as the current VMCS needs to be cleared before doing VMXOFF. Note, this results in a subtle change in ordering between disabling virtualization and stopping Intel PT on the responding CPUs. While VMX and Intel PT do interact, VMXOFF and writes to MSR_IA32_RTIT_CTL do not induce faults between one another, which is all that matters when panicking. Harden nmi_shootdown_cpus() against multiple invocations to try and capture any such kernel bugs via a WARN instead of hanging the system during a crash/dump, e.g. prior to the recent hardening of register_nmi_handler(), re-registering the NMI handler would trigger a double list_add() and hang the system if CONFIG_BUG_ON_DATA_CORRUPTION=y. list_add double add: new=ffffffff82220800, prev=ffffffff8221cfe8, next=ffffffff82220800. WARNING: CPU: 2 PID: 1319 at lib/list_debug.c:29 __list_add_valid+0x67/0x70 Call Trace: __register_nmi_handler+0xcf/0x130 nmi_shootdown_cpus+0x39/0x90 native_machine_emergency_restart+0x1c9/0x1d0 panic+0x237/0x29b Extract the disabling logic to a common helper to deduplicate code, and to prepare for doing the shootdown in the emergency reboot path if SVM is supported. Note, prior to commit ed72736183 ("x86/reboot: Force all cpus to exit VMX root if VMX is supported"), nmi_shootdown_cpus() was subtly protected against a second invocation by a cpu_vmx_enabled() check as the kdump handler would disable VMX if it ran first. Fixes: ed72736183 ("x86/reboot: Force all cpus to exit VMX root if VMX is supported") Cc: stable@vger.kernel.org Reported-by: Guilherme G. Piccoli <gpiccoli@igalia.com> Cc: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Link: https://lore.kernel.org/all/20220427224924.592546-2-gpiccoli@igalia.com Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20221130233650.1404148-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>		2023-01-24 10:05:21 -08:00
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asm	x86/crash: Disable virt in core NMI crash handler to avoid double shootdown	2023-01-24 10:05:21 -08:00
uapi/asm	KVM: x86: Replace 0-length arrays with flexible arrays	2023-01-24 10:05:18 -08:00