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From: isaku.yamahata@intel.com
To: kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Cc: isaku.yamahata@intel.com,
	isaku.yamahata@gmail.com,
	Paolo Bonzini <pbonzini@redhat.com>,
	erdemaktas@google.com,
	Sean Christopherson <seanjc@google.com>,
	Sagi Shahar <sagis@google.com>,
	Kai Huang <kai.huang@intel.com>,
	chen.bo@intel.com,
	hang.yuan@intel.com,
	tina.zhang@intel.com
Subject: [PATCH v19 079/130] KVM: TDX: vcpu_run: save/restore host state(host kernel gs)
Date: Mon, 26 Feb 2024 00:26:21 -0800
Message-Id: <4a766983346b2c01e943348af3c5ca6691e272f9.1708933498.git.isaku.yamahata@intel.com>
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From: Isaku Yamahata <isaku.yamahata@intel.com>

On entering/exiting TDX vcpu, Preserved or clobbered CPU state is different
from 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>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/main.c    | 30 +++++++++++++++++++++++++--
 arch/x86/kvm/vmx/tdx.c     | 42 ++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/tdx.h     |  4 ++++
 arch/x86/kvm/vmx/x86_ops.h |  4 ++++
 4 files changed, 78 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index d72651ce99ac..8275a242ce07 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -158,6 +158,32 @@ static void vt_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	vmx_vcpu_reset(vcpu, init_event);
 }
 
+static void vt_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * All host state is saved/restored across SEAMCALL/SEAMRET, and the
+	 * guest state of a TD is obviously off limits.  Deferring MSRs and DRs
+	 * is pointless because the TDX module needs to load *something* so as
+	 * not to expose guest state.
+	 */
+	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))
@@ -326,9 +352,9 @@ 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 = vmx_vcpu_load,
-	.vcpu_put = vmx_vcpu_put,
+	.vcpu_put = vt_vcpu_put,
 
 	.update_exception_bitmap = vmx_update_exception_bitmap,
 	.get_msr_feature = vmx_get_msr_feature,
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index fdf9196cb592..9616b1aab6ce 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/cpu.h>
+#include <linux/mmu_context.h>
 
 #include <asm/tdx.h>
 
@@ -423,6 +424,7 @@ u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
 int tdx_vcpu_create(struct kvm_vcpu *vcpu)
 {
 	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
 
 	WARN_ON_ONCE(vcpu->arch.cpuid_entries);
 	WARN_ON_ONCE(vcpu->arch.cpuid_nent);
@@ -446,9 +448,47 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
 	if ((kvm_tdx->xfam & XFEATURE_MASK_XTILE) == XFEATURE_MASK_XTILE)
 		vcpu->arch.xfd_no_write_intercept = true;
 
+	tdx->host_state_need_save = true;
+	tdx->host_state_need_restore = false;
+
 	return 0;
 }
 
+void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
+
+	if (!tdx->host_state_need_save)
+		return;
+
+	if (likely(is_64bit_mm(current->mm)))
+		tdx->msr_host_kernel_gs_base = current->thread.gsbase;
+	else
+		tdx->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
+
+	tdx->host_state_need_save = false;
+}
+
+static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
+
+	tdx->host_state_need_save = true;
+	if (!tdx->host_state_need_restore)
+		return;
+
+	++vcpu->stat.host_state_reload;
+
+	wrmsrl(MSR_KERNEL_GS_BASE, tdx->msr_host_kernel_gs_base);
+	tdx->host_state_need_restore = 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 vcpu_tdx *tdx = to_tdx(vcpu);
@@ -569,6 +609,8 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
 
 	tdx_vcpu_enter_exit(tdx);
 
+	tdx->host_state_need_restore = true;
+
 	vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
 	trace_kvm_exit(vcpu, KVM_ISA_VMX);
 
diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
index 81d301fbe638..e96c416e73bf 100644
--- a/arch/x86/kvm/vmx/tdx.h
+++ b/arch/x86/kvm/vmx/tdx.h
@@ -69,6 +69,10 @@ struct vcpu_tdx {
 
 	bool initialized;
 
+	bool host_state_need_save;
+	bool host_state_need_restore;
+	u64 msr_host_kernel_gs_base;
+
 	/*
 	 * Dummy to make pmu_intel not corrupt memory.
 	 * TODO: Support PMU for TDX.  Future work.
diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
index 3e29a6fe28ef..9fd997c79c33 100644
--- a/arch/x86/kvm/vmx/x86_ops.h
+++ b/arch/x86/kvm/vmx/x86_ops.h
@@ -151,6 +151,8 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu);
 void tdx_vcpu_free(struct kvm_vcpu *vcpu);
 void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
 fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu);
+void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
+void tdx_vcpu_put(struct kvm_vcpu *vcpu);
 u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
 
 int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
@@ -186,6 +188,8 @@ static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
 static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {}
 static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {}
 static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) { 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 u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) { return 0; }
 
 static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }
-- 
2.25.1