[PATCH v3 03/18] x86/reboot: KVM: Handle VMXOFF in KVM's reboot callback

Sean Christopherson
2023-05-12T23:50:52Z

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 a hypervisor, i.e. KVM, isn't loaded/active, i.e. if the CPU can't
possibly be post-VMXON.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/virtext.h | 10 ----------
arch/x86/kernel/reboot.c | 29 +++++++++--------------------
arch/x86/kvm/vmx/vmx.c | 8 +++++---
3 files changed, 14 insertions(+), 33 deletions(-)

diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
index 3b12e6b99412..5bc29fab15da 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 739e09527dbb..0cf2261c2dec 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -787,13 +787,7 @@ void machine_crash_shutdown(struct pt_regs *regs)
}
#endif

-/*
- * 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)
}
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();
-}
-
/* This is the CPU performing the emergency shutdown work. */
int crashing_cpu = -1;

@@ -836,9 +819,15 @@ int crashing_cpu = -1;
*/
void cpu_emergency_disable_virtualization(void)
{
- cpu_crash_vmclear_loaded_vmcss();
+ cpu_emergency_virt_cb *callback;

- cpu_emergency_vmxoff();
+ rcu_read_lock();
+ callback = rcu_dereference(cpu_emergency_virt_callback);
+ if (callback)
+ callback();
+ rcu_read_unlock();
+
+ /* 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 fc9cdb4114cc..76cdb189f1b5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -744,7 +744,7 @@ 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;
@@ -752,6 +752,8 @@ 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)
@@ -8547,7 +8549,7 @@ 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();
}
@@ -8597,7 +8599,7 @@ 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();

--
2.40.1.606.ga4b1b128d6-goog