KVM: TDX: vcpu_run: save/restore host state(host kernel gs)

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>
Message-ID: <20250129095902.16391-7-adrian.hunter@intel.com>
Reviewed-by: Xiayao Li <xiaoyao.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: yamahata

arch/x86/kvm/vmx/main.c

@@ -145,6 +145,26 @@ static void vt_update_cpu_dirty_logging(struct kvm_vcpu *vcpu)
 	vmx_update_cpu_dirty_logging(vcpu);
 }
 
+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))
@@ -265,9 +285,9 @@ 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,

arch/x86/kvm/vmx/tdx.c

@@ -3,6 +3,7 @@
 #include <linux/cpu.h>
 #include <asm/cpufeature.h>
 #include <linux/misc_cgroup.h>
+#include <linux/mmu_context.h>
 #include <asm/tdx.h>
 #include "capabilities.h"
 #include "mmu.h"
@@ -12,6 +13,7 @@
 #include "vmx.h"
 #include "mmu/spte.h"
 #include "common.h"
+#include "posted_intr.h"
 #include <trace/events/kvm.h>
 #include "trace.h"
 
@@ -629,6 +631,44 @@ 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);

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);
 
@@ -164,6 +166,8 @@ 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; }