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[PATCH v2 12/15] KVM: x86/vmx: Disable Arch LBREn bit in #DB and warm reset

Yang Weijiang posted 15 patches 3 years, 2 months ago
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[PATCH v2 12/15] KVM: x86/vmx: Disable Arch LBREn bit in #DB and warm reset
Posted by Yang Weijiang 3 years, 2 months ago 
Per SDM 3B, Chapter 18:
“On a debug breakpoint event (#DB), IA32_LBR_CTL.LBREn is cleared.”
and "On a warm reset, all LBR MSRs, including IA32_LBR_DEPTH, have their
values preserved. However, IA32_LBR_CTL.LBREn is cleared to 0, disabling
LBRs.", clear the bit manually before inject #DB or when vCPU is in warm
reset.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
 arch/x86/kvm/vmx/vmx.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 3bc892e8cf7a..6ad765ea4059 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1695,6 +1695,20 @@ static void vmx_clear_hlt(struct kvm_vcpu *vcpu)
 		vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
 }
 
+static void disable_arch_lbr_ctl(struct kvm_vcpu *vcpu)
+{
+	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
+	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
+
+	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR) &&
+	    test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use) &&
+	    lbr_desc->event) {
+		u64 ctl = vmcs_read64(GUEST_IA32_LBR_CTL);
+
+		vmcs_write64(GUEST_IA32_LBR_CTL, ctl & ~ARCH_LBR_CTL_LBREN);
+	}
+}
+
 static void vmx_inject_exception(struct kvm_vcpu *vcpu)
 {
 	struct kvm_queued_exception *ex = &vcpu->arch.exception;
@@ -1738,6 +1752,9 @@ static void vmx_inject_exception(struct kvm_vcpu *vcpu)
 	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
 
 	vmx_clear_hlt(vcpu);
+
+	if (ex->vector == DB_VECTOR)
+		disable_arch_lbr_ctl(vcpu);
 }
 
 static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr,
@@ -4796,7 +4813,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	vmx_update_fb_clear_dis(vcpu, vmx);
 
-	if (!init_event && cpu_has_vmx_arch_lbr())
+	if (init_event)
+		disable_arch_lbr_ctl(vcpu);
+	else if (cpu_has_vmx_arch_lbr())
 		vmcs_write64(GUEST_IA32_LBR_CTL, 0);
 }
 
@@ -4873,6 +4892,9 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
 			INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
 
 	vmx_clear_hlt(vcpu);
+
+	if (vcpu->arch.exception.vector == DB_VECTOR)
+		disable_arch_lbr_ctl(vcpu);
 }
 
 bool vmx_get_nmi_mask(struct kvm_vcpu *vcpu)
-- 
2.27.0
Re: [PATCH v2 12/15] KVM: x86/vmx: Disable Arch LBREn bit in #DB and warm reset
Posted by Sean Christopherson 3 years ago 
On Thu, Nov 24, 2022, Yang Weijiang wrote:
> Per SDM 3B, Chapter 18:
> “On a debug breakpoint event (#DB), IA32_LBR_CTL.LBREn is cleared.”
> and "On a warm reset, all LBR MSRs, including IA32_LBR_DEPTH, have their
> values preserved. However, IA32_LBR_CTL.LBREn is cleared to 0, disabling
> LBRs.", clear the bit manually before inject #DB or when vCPU is in warm
> reset.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 3bc892e8cf7a..6ad765ea4059 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1695,6 +1695,20 @@ static void vmx_clear_hlt(struct kvm_vcpu *vcpu)
>  		vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
>  }
>  
> +static void disable_arch_lbr_ctl(struct kvm_vcpu *vcpu)
> +{
> +	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
> +	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> +
> +	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR) &&
> +	    test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use) &&
> +	    lbr_desc->event) {

I don't see any reason to check that an event is actually assigned.  The behavior
is architectural, whether or not KVM is actively exposing LBRs to the guest is
irrelevant.

> +		u64 ctl = vmcs_read64(GUEST_IA32_LBR_CTL);
> +
> +		vmcs_write64(GUEST_IA32_LBR_CTL, ctl & ~ARCH_LBR_CTL_LBREN);
> +	}
> +}
> +
>  static void vmx_inject_exception(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm_queued_exception *ex = &vcpu->arch.exception;
> @@ -1738,6 +1752,9 @@ static void vmx_inject_exception(struct kvm_vcpu *vcpu)
>  	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
>  
>  	vmx_clear_hlt(vcpu);
> +
> +	if (ex->vector == DB_VECTOR)
> +		disable_arch_lbr_ctl(vcpu);
>  }
>  
>  static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr,
> @@ -4796,7 +4813,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  
>  	vmx_update_fb_clear_dis(vcpu, vmx);
>  
> -	if (!init_event && cpu_has_vmx_arch_lbr())
> +	if (init_event)

INIT and warm RESET are not the same thing, i.e. this is flat out wrong.

> +		disable_arch_lbr_ctl(vcpu);
> +	else if (cpu_has_vmx_arch_lbr())
>  		vmcs_write64(GUEST_IA32_LBR_CTL, 0);
>  }
>  
> @@ -4873,6 +4892,9 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
>  			INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
>  
>  	vmx_clear_hlt(vcpu);
> +
> +	if (vcpu->arch.exception.vector == DB_VECTOR)

Huh?  This is _very_ obviously injecting NMIs, not #DBs.

> +		disable_arch_lbr_ctl(vcpu);
>  }
>  
>  bool vmx_get_nmi_mask(struct kvm_vcpu *vcpu)
> -- 
> 2.27.0
>
Re: [PATCH v2 12/15] KVM: x86/vmx: Disable Arch LBREn bit in #DB and warm reset
Posted by Yang, Weijiang 3 years ago 
On 1/28/2023 6:09 AM, Sean Christopherson wrote:
> On Thu, Nov 24, 2022, Yang Weijiang wrote:
>> Per SDM 3B, Chapter 18:
>> “On a debug breakpoint event (#DB), IA32_LBR_CTL.LBREn is cleared.”
>> and "On a warm reset, all LBR MSRs, including IA32_LBR_DEPTH, have their
>> values preserved. However, IA32_LBR_CTL.LBREn is cleared to 0, disabling
>> LBRs.", clear the bit manually before inject #DB or when vCPU is in warm
>> reset.
>>
>> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>> ---
>>   arch/x86/kvm/vmx/vmx.c | 24 +++++++++++++++++++++++-
>>   1 file changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index 3bc892e8cf7a..6ad765ea4059 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -1695,6 +1695,20 @@ static void vmx_clear_hlt(struct kvm_vcpu *vcpu)
>>   		vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
>>   }
>>   
>> +static void disable_arch_lbr_ctl(struct kvm_vcpu *vcpu)
>> +{
>> +	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
>> +	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>> +
>> +	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR) &&
>> +	    test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use) &&
>> +	    lbr_desc->event) {
> I don't see any reason to check that an event is actually assigned.  The behavior
> is architectural, whether or not KVM is actively exposing LBRs to the guest is
> irrelevant

Agree, will remove them.

>
>> +		u64 ctl = vmcs_read64(GUEST_IA32_LBR_CTL);
>> +
>> +		vmcs_write64(GUEST_IA32_LBR_CTL, ctl & ~ARCH_LBR_CTL_LBREN);
>> +	}
>> +}
>> +
>>   static void vmx_inject_exception(struct kvm_vcpu *vcpu)
>>   {
>>   	struct kvm_queued_exception *ex = &vcpu->arch.exception;
>> @@ -1738,6 +1752,9 @@ static void vmx_inject_exception(struct kvm_vcpu *vcpu)
>>   	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
>>   
>>   	vmx_clear_hlt(vcpu);
>> +
>> +	if (ex->vector == DB_VECTOR)
>> +		disable_arch_lbr_ctl(vcpu);
>>   }
>>   
>>   static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr,
>> @@ -4796,7 +4813,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>   
>>   	vmx_update_fb_clear_dis(vcpu, vmx);
>>   
>> -	if (!init_event && cpu_has_vmx_arch_lbr())
>> +	if (init_event)
> INIT and warm RESET are not the same thing, i.e. this is flat out wrong.

I was confused a bit. Is there's a way to intercept guest warm RESET so 
as to disable the bit?

Or what should be followed per spec.?

>
>> +		disable_arch_lbr_ctl(vcpu);
>> +	else if (cpu_has_vmx_arch_lbr())
>>   		vmcs_write64(GUEST_IA32_LBR_CTL, 0);
>>   }
>>   
>> @@ -4873,6 +4892,9 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
>>   			INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
>>   
>>   	vmx_clear_hlt(vcpu);
>> +
>> +	if (vcpu->arch.exception.vector == DB_VECTOR)
> Huh?  This is _very_ obviously injecting NMIs, not #DBs.

My fault, will remove it.

>
>> +		disable_arch_lbr_ctl(vcpu);
>>   }
>>   
>>   bool vmx_get_nmi_mask(struct kvm_vcpu *vcpu)
>> -- 
>> 2.27.0
>>
Re: [PATCH v2 12/15] KVM: x86/vmx: Disable Arch LBREn bit in #DB and warm reset
Posted by Like Xu 3 years, 1 month ago 
On 25/11/2022 12:06 pm, Yang Weijiang wrote:
> +static void disable_arch_lbr_ctl(struct kvm_vcpu *vcpu)
> +{
> +	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
> +	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> +
> +	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR) &&
> +	    test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use) &&
> +	    lbr_desc->event) {
> +		u64 ctl = vmcs_read64(GUEST_IA32_LBR_CTL);
> +
> +		vmcs_write64(GUEST_IA32_LBR_CTL, ctl & ~ARCH_LBR_CTL_LBREN);
> +	}
> +}
> +
>   static void vmx_inject_exception(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_queued_exception *ex = &vcpu->arch.exception;
> @@ -1738,6 +1752,9 @@ static void vmx_inject_exception(struct kvm_vcpu *vcpu)
>   	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
>   
>   	vmx_clear_hlt(vcpu);
> +
> +	if (ex->vector == DB_VECTOR)
> +		disable_arch_lbr_ctl(vcpu);

Please verify this with KUT testcase, once I failed and did not confirm
if it is a hardware issue. Good Luck.

>   }
Re: [PATCH v2 12/15] KVM: x86/vmx: Disable Arch LBREn bit in #DB and warm reset
Posted by Yang, Weijiang 3 years, 1 month ago 
On 12/22/2022 7:22 PM, Like Xu wrote:
> On 25/11/2022 12:06 pm, Yang Weijiang wrote:
>> +static void disable_arch_lbr_ctl(struct kvm_vcpu *vcpu)
>> +{
>> +    struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
>> +    struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>> +
>> +    if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR) &&
>> +        test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use) &&
>> +        lbr_desc->event) {
>> +        u64 ctl = vmcs_read64(GUEST_IA32_LBR_CTL);
>> +
>> +        vmcs_write64(GUEST_IA32_LBR_CTL, ctl & ~ARCH_LBR_CTL_LBREN);
>> +    }
>> +}
>> +
>>   static void vmx_inject_exception(struct kvm_vcpu *vcpu)
>>   {
>>       struct kvm_queued_exception *ex = &vcpu->arch.exception;
>> @@ -1738,6 +1752,9 @@ static void vmx_inject_exception(struct 
>> kvm_vcpu *vcpu)
>>       vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
>>         vmx_clear_hlt(vcpu);
>> +
>> +    if (ex->vector == DB_VECTOR)
>> +        disable_arch_lbr_ctl(vcpu);
>
> Please verify this with KUT testcase, once I failed and did not confirm
> if it is a hardware issue. Good Luck.


Can  you detail what you want to verify with?



>
>>   }

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