Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Fri, 10 Mar 2023 13:42:22 -0800
In-Reply-To: <20230310214232.806108-1-seanjc@google.com>
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References: <20230310214232.806108-1-seanjc@google.com>
Message-ID: <20230310214232.806108-9-seanjc@google.com>
Subject: [PATCH v2 08/18] x86/reboot: Assert that IRQs are disabled when
 turning off virtualization
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,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Andrew Cooper <Andrew.Cooper3@citrix.com>,
        Kai Huang <kai.huang@intel.com>, Chao Gao <chao.gao@intel.com>
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Precedence: bulk

Assert that IRQs are disabled when turning off virtualization in an
emergency.  KVM enables hardware via on_each_cpu(), i.e. could re-enable
hardware if a pending IPI were delivered after disabling virtualization.

Remove a misleading comment from emergency_reboot_disable_virtualization()
about "just" needing to guarantee the CPU is stable (see above).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kernel/reboot.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index dd7def3d4144..f0d405bc718e 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -561,6 +561,13 @@ void cpu_emergency_disable_virtualization(void)
 {
 	cpu_emergency_virt_cb *callback;
 
+	/*
+	 * IRQs must be disabled as KVM enables virtualization in hardware via
+	 * function call IPIs, i.e. IRQs need to be disabled to guarantee
+	 * virtualization stays disabled.
+	 */
+	lockdep_assert_irqs_disabled();
+
 	rcu_read_lock();
 	callback = rcu_dereference(cpu_emergency_virt_callback);
 	if (callback)
@@ -570,7 +577,6 @@ void cpu_emergency_disable_virtualization(void)
 
 static void emergency_reboot_disable_virtualization(void)
 {
-	/* Just make sure we won't change CPUs while doing this */
 	local_irq_disable();
 
 	/*
-- 
2.40.0.rc1.284.g88254d51c5-goog