linux-kernel - [PATCH 05/16] x86/reboot: KVM: Handle VMXOFF in KVM's reboot callback

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Message-ID: <20221201232655.290720-6-seanjc@google.com>
Date:   Thu,  1 Dec 2022 23:26:44 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Andrew Cooper <Andrew.Cooper3@...rix.com>
Subject: [PATCH 05/16] x86/reboot: KVM: Handle VMXOFF in KVM's reboot callback

Use KVM VMX's reboot/crash callback to do VMXOFF in an emergency instead
of manually and blindly doing VMXOFF.  There's no need to attempt VMXOFF
if KVM (or some other out-of-tree hypervisor) isn't loaded/active, i.e.
if the CPU can't possibly be post-VMXON.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/virtext.h | 10 ----------
 arch/x86/kernel/reboot.c       | 30 +++++++++---------------------
 arch/x86/kvm/vmx/vmx.c         |  8 +++++---
 3 files changed, 14 insertions(+), 34 deletions(-)

diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
index 0acb14806a74..4f61283b1f52 100644
--- a/arch/x86/include/asm/virtext.h
+++ b/arch/x86/include/asm/virtext.h
@@ -70,16 +70,6 @@ static inline void __cpu_emergency_vmxoff(void)
 		cpu_vmxoff();
 }
 
-/** Disable VMX if it is supported and enabled on the current CPU
- */
-static inline void cpu_emergency_vmxoff(void)
-{
-	if (cpu_has_vmx())
-		__cpu_emergency_vmxoff();
-}
-
-
-
 
 /*
  * SVM functions:
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 40ea16ecb3b8..85ea1fdebf4c 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -788,13 +788,7 @@ void machine_crash_shutdown(struct pt_regs *regs)
 #endif
 
 #if IS_ENABLED(CONFIG_KVM_INTEL)
-/*
- * This is used to VMCLEAR all VMCSs loaded on the
- * processor. And when loading kvm_intel module, the
- * callback function pointer will be assigned.
- *
- * protected by rcu.
- */
+/* RCU-protected callback to disable virtualization prior to reboot. */
 static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback;
 
 void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback)
@@ -815,17 +809,6 @@ void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback)
 	synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(cpu_emergency_unregister_virt_callback);
-
-static inline void cpu_crash_vmclear_loaded_vmcss(void)
-{
-	cpu_emergency_virt_cb *callback;
-
-	rcu_read_lock();
-	callback = rcu_dereference(cpu_emergency_virt_callback);
-	if (callback)
-		callback();
-	rcu_read_unlock();
-}
 #endif
 
 /* This is the CPU performing the emergency shutdown work. */
@@ -841,10 +824,15 @@ void cpu_emergency_disable_virtualization(void)
 	lockdep_assert_irqs_disabled();
 
 #if IS_ENABLED(CONFIG_KVM_INTEL)
-	cpu_crash_vmclear_loaded_vmcss();
-#endif
+	cpu_emergency_virt_cb *callback;
 
-	cpu_emergency_vmxoff();
+	rcu_read_lock();
+	callback = rcu_dereference(cpu_emergency_virt_callback);
+	if (callback)
+		callback();
+	rcu_read_unlock();
+#endif
+	/* KVM_AMD doesn't yet utilize the common callback. */
 	cpu_emergency_svm_disable();
 }
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 6e0cc4d03884..6f3ade75a670 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -743,7 +743,7 @@ static int vmx_set_guest_uret_msr(struct vcpu_vmx *vmx,
 	return ret;
 }
 
-static void crash_vmclear_local_loaded_vmcss(void)
+static void vmx_emergency_disable(void)
 {
 	int cpu = raw_smp_processor_id();
 	struct loaded_vmcs *v;
@@ -751,6 +751,8 @@ static void crash_vmclear_local_loaded_vmcss(void)
 	list_for_each_entry(v, &per_cpu(loaded_vmcss_on_cpu, cpu),
 			    loaded_vmcss_on_cpu_link)
 		vmcs_clear(v->vmcs);
+
+	__cpu_emergency_vmxoff();
 }
 
 static void __loaded_vmcs_clear(void *arg)
@@ -8526,7 +8528,7 @@ static void __vmx_exit(void)
 {
 	allow_smaller_maxphyaddr = false;
 
-	cpu_emergency_unregister_virt_callback(crash_vmclear_local_loaded_vmcss);
+	cpu_emergency_unregister_virt_callback(vmx_emergency_disable);
 
 	vmx_cleanup_l1d_flush();
 }
@@ -8576,7 +8578,7 @@ static int __init vmx_init(void)
 		pi_init_cpu(cpu);
 	}
 
-	cpu_emergency_register_virt_callback(crash_vmclear_local_loaded_vmcss);
+	cpu_emergency_register_virt_callback(vmx_emergency_disable);
 
 	vmx_check_vmcs12_offsets();
 
-- 
2.39.0.rc0.267.gcb52ba06e7-goog