[PATCH V2 06/12] KVM: TDX: vcpu_run: save/restore host state(host kernel gs)

Adrian Hunter
2025-01-29T10:00:15Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

On entering/exiting TDX vcpu, preserved or clobbered CPU state is different
from the VMX case. Add TDX hooks to save/restore host/guest CPU state.
Save/restore kernel GS base MSR.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
TD vcpu enter/exit v2:
- Use 1 variable named 'guest_state_loaded' to track host state
save/restore (Sean)
- Rebased due to moving guest_state_loaded/msr_host_kernel_gs_base
to struct vcpu_vt.

TD vcpu enter/exit v1:
- Clarify comment (Binbin)
- Use lower case preserved and add the for VMX in log (Tony)
- Fix bisectability issue with includes (Kai)
---
arch/x86/kvm/vmx/main.c | 24 +++++++++++++++++++++--
arch/x86/kvm/vmx/tdx.c | 40 ++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/vmx/x86_ops.h | 4 ++++
3 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index 301c1a26606f..341aa537ca72 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -133,6 +133,26 @@ static void vt_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
vmx_vcpu_load(vcpu, cpu);
}

+static void vt_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
+{
+ if (is_td_vcpu(vcpu)) {
+ tdx_prepare_switch_to_guest(vcpu);
+ return;
+ }
+
+ vmx_prepare_switch_to_guest(vcpu);
+}
+
+static void vt_vcpu_put(struct kvm_vcpu *vcpu)
+{
+ if (is_td_vcpu(vcpu)) {
+ tdx_vcpu_put(vcpu);
+ return;
+ }
+
+ vmx_vcpu_put(vcpu);
+}
+
static int vt_vcpu_pre_run(struct kvm_vcpu *vcpu)
{
if (is_td_vcpu(vcpu))
@@ -253,9 +273,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.vcpu_free = vt_vcpu_free,
.vcpu_reset = vt_vcpu_reset,

- .prepare_switch_to_guest = vmx_prepare_switch_to_guest,
+ .prepare_switch_to_guest = vt_prepare_switch_to_guest,
.vcpu_load = vt_vcpu_load,
- .vcpu_put = vmx_vcpu_put,
+ .vcpu_put = vt_vcpu_put,

.update_exception_bitmap = vmx_update_exception_bitmap,
.get_feature_msr = vmx_get_feature_msr,
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 95420ffd0022..3f3d61935a58 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2,6 +2,7 @@
#include <linux/cleanup.h>
#include <linux/cpu.h>
#include <asm/cpufeature.h>
+#include <linux/mmu_context.h>
#include <asm/tdx.h>
#include "capabilities.h"
#include "mmu.h"
@@ -11,6 +12,7 @@
#include "vmx.h"
#include "mmu/spte.h"
#include "common.h"
+#include "posted_intr.h"
#include <trace/events/kvm.h>
#include "trace.h"

@@ -642,6 +644,44 @@ void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
local_irq_enable();
}

+/*
+ * Compared to vmx_prepare_switch_to_guest(), there is not much to do
+ * as SEAMCALL/SEAMRET calls take care of most of save and restore.
+ */
+void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_vt *vt = to_vt(vcpu);
+
+ if (vt->guest_state_loaded)
+ return;
+
+ if (likely(is_64bit_mm(current->mm)))
+ vt->msr_host_kernel_gs_base = current->thread.gsbase;
+ else
+ vt->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
+
+ vt->guest_state_loaded = true;
+}
+
+static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_vt *vt = to_vt(vcpu);
+
+ if (!vt->guest_state_loaded)
+ return;
+
+ ++vcpu->stat.host_state_reload;
+ wrmsrl(MSR_KERNEL_GS_BASE, vt->msr_host_kernel_gs_base);
+
+ vt->guest_state_loaded = false;
+}
+
+void tdx_vcpu_put(struct kvm_vcpu *vcpu)
+{
+ vmx_vcpu_pi_put(vcpu);
+ tdx_prepare_switch_to_host(vcpu);
+}
+
void tdx_vcpu_free(struct kvm_vcpu *vcpu)
{
struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
index 83aac44b779b..f856eac8f1e8 100644
--- a/arch/x86/kvm/vmx/x86_ops.h
+++ b/arch/x86/kvm/vmx/x86_ops.h
@@ -133,6 +133,8 @@ void tdx_vcpu_free(struct kvm_vcpu *vcpu);
void tdx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu);
fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit);
+void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
+void tdx_vcpu_put(struct kvm_vcpu *vcpu);

int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);

@@ -165,6 +167,8 @@ static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediat
{
return EXIT_FASTPATH_NONE;
}
+static inline void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) {}
+static inline void tdx_vcpu_put(struct kvm_vcpu *vcpu) {}

static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }

--
2.43.0