diff mbox series

[v17,072/116] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior

Message ID 8f7c06228a0e7c2300ac7e4d074097e120f6aadf.1699368322.git.isaku.yamahata@intel.com (mailing list archive)
State New, archived
Headers show
Series KVM TDX basic feature support | expand

Commit Message

Isaku Yamahata Nov. 7, 2023, 2:56 p.m. UTC 
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 | 10 ++++++++--
 arch/x86/kvm/vmx/tdx.c          |  1 +
 arch/x86/kvm/x86.c              | 11 ++++++++---
 3 files changed, 17 insertions(+), 5 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 033254717839..29c714560627 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -610,8 +610,14 @@  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 (DR0-3 and DR6) are saved/restored by hardware
+	 * on exit from or enter to guest. KVM needn't switch them. Because DR7
+	 * is cleared on exit from guest, DR7 need to be saved/restored.
+	 */
+	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 af05611ddde5..fc21cfc6914d 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -560,6 +560,7 @@  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 a1b2e80d7051..a67f78ab8f8e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10914,7 +10914,7 @@  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);
@@ -10960,6 +10960,7 @@  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);
@@ -10972,8 +10973,12 @@  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());