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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>,
        Xiaoyao Li <xiaoyao.li@intel.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Chao Gao <chao.gao@intel.com>
Subject: [PATCH v9 074/105] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior
Date:   Fri, 30 Sep 2022 03:18:08 -0700
Message-Id: <d5d1cf06c33626c3fb35820703ba947cd310b804.1664530908.git.isaku.yamahata@intel.com>
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From: Isaku Yamahata <isaku.yamahata@intel.com>

Add a flag, KVM_DEBUGREG_AUTO_SWITCHED_GUEST, to skip saving/restoring DRs
irrespective of any other flags.  TDX-SEAM unconditionally saves and
restores guest DRs and reset to architectural INIT state on TD exit.
So, KVM needs to save host DRs before TD enter without restoring guest DRs
and restore host DRs after TD exit.

Opportunistically convert the KVM_DEBUGREG_* definitions to use BIT().

Reported-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/include/asm/kvm_host.h |  9 +++++++--
 arch/x86/kvm/vmx/tdx.c          |  1 +
 arch/x86/kvm/x86.c              | 11 ++++++++---
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e772798684ae..e29a93973ad8 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -584,8 +584,13 @@ struct kvm_pmu {
 struct kvm_pmu_ops;
 
 enum {
-	KVM_DEBUGREG_BP_ENABLED = 1,
-	KVM_DEBUGREG_WONT_EXIT = 2,
+	KVM_DEBUGREG_BP_ENABLED		= BIT(0),
+	KVM_DEBUGREG_WONT_EXIT		= BIT(1),
+	/*
+	 * Guest debug registers are saved/restored by hardware on exit from
+	 * or enter guest. KVM needn't switch them.
+	 */
+	KVM_DEBUGREG_AUTO_SWITCH	= BIT(2),
 };
 
 struct kvm_mtrr_range {
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 51de41fbe098..78322bd6037e 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -421,6 +421,7 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
 
 	vcpu->arch.efer = EFER_SCE | EFER_LME | EFER_LMA | EFER_NX;
 
+	vcpu->arch.switch_db_regs = KVM_DEBUGREG_AUTO_SWITCH;
 	vcpu->arch.cr0_guest_owned_bits = -1ul;
 	vcpu->arch.cr4_guest_owned_bits = -1ul;
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8160f51bbb92..fda72bef6c90 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10540,7 +10540,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	if (vcpu->arch.guest_fpu.xfd_err)
 		wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
 
-	if (unlikely(vcpu->arch.switch_db_regs)) {
+	if (unlikely(vcpu->arch.switch_db_regs & ~KVM_DEBUGREG_AUTO_SWITCH)) {
 		set_debugreg(0, 7);
 		set_debugreg(vcpu->arch.eff_db[0], 0);
 		set_debugreg(vcpu->arch.eff_db[1], 1);
@@ -10583,6 +10583,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	 */
 	if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)) {
 		WARN_ON(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP);
+		WARN_ON(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH);
 		static_call(kvm_x86_sync_dirty_debug_regs)(vcpu);
 		kvm_update_dr0123(vcpu);
 		kvm_update_dr7(vcpu);
@@ -10595,8 +10596,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	 * care about the messed up debug address registers. But if
 	 * we have some of them active, restore the old state.
 	 */
-	if (hw_breakpoint_active())
-		hw_breakpoint_restore();
+	if (hw_breakpoint_active()) {
+		if (!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH))
+			hw_breakpoint_restore();
+		else
+			set_debugreg(__this_cpu_read(cpu_dr7), 7);
+	}
 
 	vcpu->arch.last_vmentry_cpu = vcpu->cpu;
 	vcpu->arch.last_guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
-- 
2.25.1