linux-kernel - [PATCH v3 04/10] KVM: TDX: vcpu_run: save/restore host state(host kernel gs)

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Message-ID: <20250307212053.2948340-5-pbonzini@redhat.com>
Date: Fri,  7 Mar 2025 16:20:46 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: xiaoyao.li@...el.com,
	adrian.hunter@...el.com,
	seanjc@...gle.com,
	rick.p.edgecombe@...el.com,
	Isaku Yamahata <isaku.yamahata@...el.com>
Subject: [PATCH v3 04/10] KVM: TDX: vcpu_run: save/restore host state(host kernel gs)

From: Isaku Yamahata <isaku.yamahata@...el.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@...el.com>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
Message-ID: <20250129095902.16391-7-adrian.hunter@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 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 037590fc05e9..c0497ed0c9be 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/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,
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index f50565f45b6a..94e08fdcb775 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/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"
 
@@ -624,6 +626,44 @@ 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 578c26d3aec4..cd18e9b1e124 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);
 
@@ -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; }
 
-- 
2.43.5