diff mbox series

[v18,077/121] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior

Message ID 6ae14d4e3a2f248879dcfc2990816f6341458c40.1705965635.git.isaku.yamahata@intel.com (mailing list archive)
State New, archived
Headers show
Series KVM TDX basic feature support | expand

Commit Message

Isaku Yamahata Jan. 22, 2024, 11:53 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(-)

Comments

Binbin Wu Feb. 26, 2024, 1:27 a.m. UTC | #1 
On 1/23/2024 7:53 AM, isaku.yamahata@intel.com wrote:
> 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.

The description here is different from the implementation.
The changelog needs to be updated?

>
> 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 --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 5cb25e1f83ce..a7782a6f995a 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -626,8 +626,14 @@ 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 58583f0ab131..db01162de136 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -636,6 +636,7 @@ 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 f14e3e888842..e252372bb633 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10973,7 +10973,7 @@ 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);
> @@ -11019,6 +11019,7 @@ 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);
> @@ -11031,8 +11032,12 @@ 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());
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5cb25e1f83ce..a7782a6f995a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -626,8 +626,14 @@  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 58583f0ab131..db01162de136 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -636,6 +636,7 @@  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 f14e3e888842..e252372bb633 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10973,7 +10973,7 @@  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);
@@ -11019,6 +11019,7 @@  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);
@@ -11031,8 +11032,12 @@  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());