[PATCH v3 04/18] x86/reboot: KVM: Disable SVM during reboot via virt/KVM reboot callback

Sean Christopherson
2023-05-12T23:50:56Z

Use the virt callback to disable SVM (and set GIF=1) during an emergency
instead of blindly attempting to disable SVM. Like the VMX case, if a
hypervisor, i.e. KVM, isn't loaded/active, SVM can't be in use.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/virtext.h | 8 --------
arch/x86/kernel/reboot.c | 3 ---
arch/x86/kvm/svm/svm.c | 19 +++++++++++++++++--
3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
index 5bc29fab15da..aaed66249ccf 100644
--- a/arch/x86/include/asm/virtext.h
+++ b/arch/x86/include/asm/virtext.h
@@ -133,12 +133,4 @@ static inline void cpu_svm_disable(void)
}
}

-/** Makes sure SVM is disabled, if it is supported on the CPU
- */
-static inline void cpu_emergency_svm_disable(void)
-{
- if (cpu_has_svm(NULL))
- cpu_svm_disable();
-}
-
#endif /* _ASM_X86_VIRTEX_H */
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 0cf2261c2dec..92b380e199a3 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -826,9 +826,6 @@ void cpu_emergency_disable_virtualization(void)
if (callback)
callback();
rcu_read_unlock();
-
- /* KVM_AMD doesn't yet utilize the common callback. */
- cpu_emergency_svm_disable();
}

#if defined(CONFIG_SMP)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index eb308c9994f9..0f0d04900bf2 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -38,6 +38,7 @@
#include <asm/spec-ctrl.h>
#include <asm/cpu_device_id.h>
#include <asm/traps.h>
+#include <asm/reboot.h>
#include <asm/fpu/api.h>

#include <asm/virtext.h>
@@ -568,6 +569,11 @@ void __svm_write_tsc_multiplier(u64 multiplier)
preempt_enable();
}

+static void svm_emergency_disable(void)
+{
+ cpu_svm_disable();
+}
+
static void svm_hardware_disable(void)
{
/* Make sure we clean up behind us */
@@ -5184,6 +5190,13 @@ static struct kvm_x86_init_ops svm_init_ops __initdata = {
.pmu_ops = &amd_pmu_ops,
};

+static void __svm_exit(void)
+{
+ kvm_x86_vendor_exit();
+
+ cpu_emergency_unregister_virt_callback(svm_emergency_disable);
+}
+
static int __init svm_init(void)
{
int r;
@@ -5197,6 +5210,8 @@ static int __init svm_init(void)
if (r)
return r;

+ cpu_emergency_register_virt_callback(svm_emergency_disable);
+
/*
* Common KVM initialization _must_ come last, after this, /dev/kvm is
* exposed to userspace!
@@ -5209,14 +5224,14 @@ static int __init svm_init(void)
return 0;

err_kvm_init:
- kvm_x86_vendor_exit();
+ __svm_exit();
return r;
}

static void __exit svm_exit(void)
{
kvm_exit();
- kvm_x86_vendor_exit();
+ __svm_exit();
}

module_init(svm_init)
--
2.40.1.606.ga4b1b128d6-goog