Commit 484612f1 authored Jan 29, 2025 by Isaku Yamahata Committed by Paolo Bonzini Mar 14, 2025

KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior



Add a flag KVM_DEBUGREG_AUTO_SWITCH to skip saving/restoring guest
DRs.

TDX-SEAM unconditionally saves/restores guest DRs on TD exit/enter,
and resets DRs to architectural INIT state on TD exit.  Use the new
flag KVM_DEBUGREG_AUTO_SWITCH to indicate that KVM doesn't need to
save/restore guest DRs.  KVM still needs to restore host DRs after TD
exit if there are active breakpoints in the host, which is covered by
the existing code.

MOV-DR exiting is always cleared for TDX guests, so the handler for DR
access is never called, and KVM_DEBUGREG_WONT_EXIT is never set.  Add
a warning if both KVM_DEBUGREG_WONT_EXIT and KVM_DEBUGREG_AUTO_SWITCH
are set.

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>
[binbin: rework changelog]
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Message-ID: <20241210004946.3718496-2-binbin.wu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20250129095902.16391-13-adrian.hunter@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 8af09903

arch/x86/include/asm/kvm_host.h

+9 −2

Original line number	Diff line number	Diff line
		@@ -606,8 +606,15 @@ 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, DR6 and DR7) are saved/restored by
		* hardware on exit from or enter to guest. KVM needn't switch them.
		* DR0-3, DR6 and DR7 are set to their architectural INIT value on VM
		* exit, host values need to be restored.
		*/
		KVM_DEBUGREG_AUTO_SWITCH = BIT(2),
		};

		struct kvm_mtrr {

arch/x86/kvm/vmx/tdx.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -630,6 +630,7 @@ 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;

arch/x86/kvm/x86.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -10985,7 +10985,8 @@ 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 &&
		!(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);
		@@ -11037,6 +11038,7 @@ 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);
		kvm_x86_call(sync_dirty_debug_regs)(vcpu);
		kvm_update_dr0123(vcpu);
		kvm_update_dr7(vcpu);