Re: [PATCH v2 0/3] x86/crash: Fix double NMI shootdown bug

From: Guilherme G. Piccoli
Date: Mon Oct 03 2022 - 12:04:52 EST

On 17/05/2022 21:16, Sean Christopherson wrote:
> 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 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.
> Patch 2 is a related bug fix found while exploring ideas for patch 1.
> Patch 3 is a cleanup to try to prevent future "fixed VMX but not SVM"
> style bugs.
> Guilherme and Vitaly, I dropped your Tested-by and Reviewed-by tags
> since the relevant patches changed a decent amount.
> 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().
> v1:
> Sean Christopherson (3):
> x86/crash: Disable virt in core NMI crash handler to avoid double
> shootdown
> x86/reboot: Disable virtualization in an emergency if SVM is supported
> x86/virt: Fold __cpu_emergency_vmxoff() into its sole caller
> arch/x86/include/asm/reboot.h | 1 +
> arch/x86/include/asm/virtext.h | 14 +-----
> arch/x86/kernel/crash.c | 16 +-----
> arch/x86/kernel/reboot.c | 89 +++++++++++++++++++++++++---------
> 4 files changed, 69 insertions(+), 51 deletions(-)
> base-commit: a7fed5c0431dbfa707037848830f980e0f93cfb3

Hi folks, monthly ping!
Any news on this fix series? Just checked, still applies cleanly.