diff mbox series

[RFC,v2,36/69] KVM: x86: Add a switch_db_regs flag to handle TDX's auto-switched behavior

Message ID 1f79ce2ad686f25767711ccd6a520324dd6e1c21.1625186503.git.isaku.yamahata@intel.com (mailing list archive)
State New, archived
Headers show
Series KVM: X86: TDX support | expand

Commit Message

Isaku Yamahata July 2, 2021, 10:04 p.m. UTC 
From: Sean Christopherson <sean.j.christopherson@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 | 11 ++++++++---
 arch/x86/kvm/x86.c              |  3 ++-
 2 files changed, 10 insertions(+), 4 deletions(-)

Comments

Paolo Bonzini July 6, 2021, 2:36 p.m. UTC | #1 
On 03/07/21 00:04, isaku.yamahata@intel.com wrote:
> From: Sean Christopherson <sean.j.christopherson@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 | 11 ++++++++---
>   arch/x86/kvm/x86.c              |  3 ++-
>   2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 96e6cd95d884..7822b531a5e2 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -488,9 +488,14 @@ struct kvm_pmu {
>   struct kvm_pmu_ops;
>   
>   enum {
> -	KVM_DEBUGREG_BP_ENABLED = 1,
> -	KVM_DEBUGREG_WONT_EXIT = 2,
> -	KVM_DEBUGREG_RELOAD = 4,
> +	KVM_DEBUGREG_BP_ENABLED		= BIT(0),
> +	KVM_DEBUGREG_WONT_EXIT		= BIT(1),
> +	KVM_DEBUGREG_RELOAD		= BIT(2),
> +	/*
> +	 * Guest debug registers are saved/restored by hardware on exit from
> +	 * or enter guest. KVM needn't switch them.
> +	 */
> +	KVM_DEBUGREG_AUTO_SWITCH_GUEST	= BIT(3),

Maybe remove "_GUEST"?  Apart from that,

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

>   };
>   
>   struct kvm_mtrr_range {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4b436cae1732..f1d5e0a53640 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9441,7 +9441,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   	if (test_thread_flag(TIF_NEED_FPU_LOAD))
>   		switch_fpu_return();
>   
> -	if (unlikely(vcpu->arch.switch_db_regs)) {
> +	if (unlikely(vcpu->arch.switch_db_regs & ~KVM_DEBUGREG_AUTO_SWITCH_GUEST)) {
>   		set_debugreg(0, 7);
>   		set_debugreg(vcpu->arch.eff_db[0], 0);
>   		set_debugreg(vcpu->arch.eff_db[1], 1);
> @@ -9473,6 +9473,7 @@ 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_GUEST);
>   		static_call(kvm_x86_sync_dirty_debug_regs)(vcpu);
>   		kvm_update_dr0123(vcpu);
>   		kvm_update_dr7(vcpu);
>
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 96e6cd95d884..7822b531a5e2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -488,9 +488,14 @@  struct kvm_pmu {
 struct kvm_pmu_ops;
 
 enum {
-	KVM_DEBUGREG_BP_ENABLED = 1,
-	KVM_DEBUGREG_WONT_EXIT = 2,
-	KVM_DEBUGREG_RELOAD = 4,
+	KVM_DEBUGREG_BP_ENABLED		= BIT(0),
+	KVM_DEBUGREG_WONT_EXIT		= BIT(1),
+	KVM_DEBUGREG_RELOAD		= BIT(2),
+	/*
+	 * Guest debug registers are saved/restored by hardware on exit from
+	 * or enter guest. KVM needn't switch them.
+	 */
+	KVM_DEBUGREG_AUTO_SWITCH_GUEST	= BIT(3),
 };
 
 struct kvm_mtrr_range {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4b436cae1732..f1d5e0a53640 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9441,7 +9441,7 @@  static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	if (test_thread_flag(TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
 
-	if (unlikely(vcpu->arch.switch_db_regs)) {
+	if (unlikely(vcpu->arch.switch_db_regs & ~KVM_DEBUGREG_AUTO_SWITCH_GUEST)) {
 		set_debugreg(0, 7);
 		set_debugreg(vcpu->arch.eff_db[0], 0);
 		set_debugreg(vcpu->arch.eff_db[1], 1);
@@ -9473,6 +9473,7 @@  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_GUEST);
 		static_call(kvm_x86_sync_dirty_debug_regs)(vcpu);
 		kvm_update_dr0123(vcpu);
 		kvm_update_dr7(vcpu);