From: Sean Christopherson <seanjc@google.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org,
"Guilherme G . Piccoli" <gpiccoli@igalia.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>
Subject: [PATCH v2 0/3] x86/crash: Fix double NMI shootdown bug
Date: Wed, 18 May 2022 00:16:44 +0000 [thread overview]
Message-ID: <20220518001647.1291448-1-seanjc@google.com> (raw)
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.
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: https://lore.kernel.org/all/20220511234332.3654455-1-seanjc@google.com
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
--
2.36.0.550.gb090851708-goog
next reply other threads:[~2022-05-18 0:16 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-18 0:16 Sean Christopherson [this message]
2022-05-18 0:16 ` [PATCH v2 1/3] x86/crash: Disable virt in core NMI crash handler to avoid double shootdown Sean Christopherson
2022-05-18 15:50 ` Guilherme G. Piccoli
2022-05-18 0:16 ` [PATCH v2 2/3] x86/reboot: Disable virtualization in an emergency if SVM is supported Sean Christopherson
2022-05-18 0:16 ` [PATCH v2 3/3] x86/virt: Fold __cpu_emergency_vmxoff() into its sole caller Sean Christopherson
2022-06-03 16:07 ` [PATCH v2 0/3] x86/crash: Fix double NMI shootdown bug Guilherme G. Piccoli
2022-07-08 23:28 ` Sean Christopherson
2022-08-22 18:39 ` Guilherme G. Piccoli
2022-10-03 16:03 ` Guilherme G. Piccoli
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