* [PATCH] KVM: x86: Trace changes to active TSC offset regardless if vCPU in guest-mode
@ 2018-11-25 17:53 Paolo Bonzini
2018-11-25 21:38 ` Liran Alon
0 siblings, 1 reply; 4+ messages in thread
From: Paolo Bonzini @ 2018-11-25 17:53 UTC (permalink / raw)
To: linux-kernel, kvm; +Cc: Liran Alon, Jim Mattson
For some reason, kvm_x86_ops->write_l1_tsc_offset() skipped trace
of change to active TSC offset in case vCPU is in guest-mode.
This patch changes write_l1_tsc_offset() behavior to trace any change
to active TSC offset to aid debugging. The VMX code is changed to
look more similar to SVM, which is in my opinion nicer.
Based on a patch by Liran Alon.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
Untested still, but throwing it out because it seems pretty
obvious...
arch/x86/kvm/svm.c | 9 +++++----
arch/x86/kvm/vmx.c | 34 +++++++++++++++++-----------------
2 files changed, 22 insertions(+), 21 deletions(-)
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index a24733aade4c..0d1a74069a9e 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1456,10 +1456,11 @@ static u64 svm_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
g_tsc_offset = svm->vmcb->control.tsc_offset -
svm->nested.hsave->control.tsc_offset;
svm->nested.hsave->control.tsc_offset = offset;
- } else
- trace_kvm_write_tsc_offset(vcpu->vcpu_id,
- svm->vmcb->control.tsc_offset,
- offset);
+ }
+
+ trace_kvm_write_tsc_offset(vcpu->vcpu_id,
+ svm->vmcb->control.tsc_offset - g_tsc_offset,
+ offset);
svm->vmcb->control.tsc_offset = offset + g_tsc_offset;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 764c23dc444f..e7d3f7d35355 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3466,24 +3466,24 @@ static u64 vmx_read_l1_tsc_offset(struct kvm_vcpu *vcpu)
static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
{
- u64 active_offset = offset;
- if (is_guest_mode(vcpu)) {
- /*
- * We're here if L1 chose not to trap WRMSR to TSC. According
- * to the spec, this should set L1's TSC; The offset that L1
- * set for L2 remains unchanged, and still needs to be added
- * to the newly set TSC to get L2's TSC.
- */
- struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
- if (nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING))
- active_offset += vmcs12->tsc_offset;
- } else {
- trace_kvm_write_tsc_offset(vcpu->vcpu_id,
- vmcs_read64(TSC_OFFSET), offset);
- }
+ struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+ u64 g_tsc_offset = 0;
+
+ /*
+ * We're here if L1 chose not to trap WRMSR to TSC. According
+ * to the spec, this should set L1's TSC; The offset that L1
+ * set for L2 remains unchanged, and still needs to be added
+ * to the newly set TSC to get L2's TSC.
+ */
+ if (is_guest_mode(vcpu) &&
+ (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING))
+ g_tsc_offset = vmcs12->tsc_offset;
- vmcs_write64(TSC_OFFSET, active_offset);
- return active_offset;
+ trace_kvm_write_tsc_offset(vcpu->vcpu_id,
+ vcpu->arch.tsc_offset - g_tsc_offset,
+ offset);
+ vmcs_write64(TSC_OFFSET, offset + g_tsc_offset);
+ return offset + g_tsc_offset;
}
/*
--
1.8.3.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: x86: Trace changes to active TSC offset regardless if vCPU in guest-mode
2018-11-25 17:53 [PATCH] KVM: x86: Trace changes to active TSC offset regardless if vCPU in guest-mode Paolo Bonzini
@ 2018-11-25 21:38 ` Liran Alon
2018-11-26 10:27 ` Paolo Bonzini
2018-11-26 10:27 ` Paolo Bonzini
0 siblings, 2 replies; 4+ messages in thread
From: Liran Alon @ 2018-11-25 21:38 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: linux-kernel, kvm, Jim Mattson
> On 25 Nov 2018, at 19:53, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> For some reason, kvm_x86_ops->write_l1_tsc_offset() skipped trace
> of change to active TSC offset in case vCPU is in guest-mode.
> This patch changes write_l1_tsc_offset() behavior to trace any change
> to active TSC offset to aid debugging. The VMX code is changed to
> look more similar to SVM, which is in my opinion nicer.
>
> Based on a patch by Liran Alon.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
I would have applied this refactoring change on top of my original version of this patch. Easier to read and review.
But I guess it’s a matter of taste…
Anyway, code looks correct to me. Therefore:
Reviewed-by: Liran Alon <liran.alon@oracle.com>
> ---
> Untested still, but throwing it out because it seems pretty
> obvious...
>
> arch/x86/kvm/svm.c | 9 +++++----
> arch/x86/kvm/vmx.c | 34 +++++++++++++++++-----------------
> 2 files changed, 22 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index a24733aade4c..0d1a74069a9e 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1456,10 +1456,11 @@ static u64 svm_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> g_tsc_offset = svm->vmcb->control.tsc_offset -
> svm->nested.hsave->control.tsc_offset;
> svm->nested.hsave->control.tsc_offset = offset;
> - } else
> - trace_kvm_write_tsc_offset(vcpu->vcpu_id,
> - svm->vmcb->control.tsc_offset,
> - offset);
> + }
> +
> + trace_kvm_write_tsc_offset(vcpu->vcpu_id,
> + svm->vmcb->control.tsc_offset - g_tsc_offset,
> + offset);
>
> svm->vmcb->control.tsc_offset = offset + g_tsc_offset;
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 764c23dc444f..e7d3f7d35355 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3466,24 +3466,24 @@ static u64 vmx_read_l1_tsc_offset(struct kvm_vcpu *vcpu)
>
> static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> {
> - u64 active_offset = offset;
> - if (is_guest_mode(vcpu)) {
> - /*
> - * We're here if L1 chose not to trap WRMSR to TSC. According
> - * to the spec, this should set L1's TSC; The offset that L1
> - * set for L2 remains unchanged, and still needs to be added
> - * to the newly set TSC to get L2's TSC.
> - */
> - struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> - if (nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING))
> - active_offset += vmcs12->tsc_offset;
> - } else {
> - trace_kvm_write_tsc_offset(vcpu->vcpu_id,
> - vmcs_read64(TSC_OFFSET), offset);
> - }
> + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> + u64 g_tsc_offset = 0;
> +
> + /*
> + * We're here if L1 chose not to trap WRMSR to TSC. According
> + * to the spec, this should set L1's TSC; The offset that L1
> + * set for L2 remains unchanged, and still needs to be added
> + * to the newly set TSC to get L2's TSC.
> + */
> + if (is_guest_mode(vcpu) &&
> + (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING))
> + g_tsc_offset = vmcs12->tsc_offset;
>
> - vmcs_write64(TSC_OFFSET, active_offset);
> - return active_offset;
> + trace_kvm_write_tsc_offset(vcpu->vcpu_id,
> + vcpu->arch.tsc_offset - g_tsc_offset,
> + offset);
> + vmcs_write64(TSC_OFFSET, offset + g_tsc_offset);
> + return offset + g_tsc_offset;
> }
>
> /*
> --
> 1.8.3.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: x86: Trace changes to active TSC offset regardless if vCPU in guest-mode
2018-11-25 21:38 ` Liran Alon
@ 2018-11-26 10:27 ` Paolo Bonzini
2018-11-26 10:27 ` Paolo Bonzini
1 sibling, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2018-11-26 10:27 UTC (permalink / raw)
To: Liran Alon; +Cc: linux-kernel, kvm, Jim Mattson
On 25/11/18 22:38, Liran Alon wrote:
>
>
>> On 25 Nov 2018, at 19:53, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> For some reason, kvm_x86_ops->write_l1_tsc_offset() skipped trace
>> of change to active TSC offset in case vCPU is in guest-mode.
>> This patch changes write_l1_tsc_offset() behavior to trace any change
>> to active TSC offset to aid debugging. The VMX code is changed to
>> look more similar to SVM, which is in my opinion nicer.
>>
>> Based on a patch by Liran Alon.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>
> I would have applied this refactoring change on top of my original version of this patch. Easier to read and review.
Your original version of the patch is a bit different, in that it traced
the L2 TSC offset for vmx and the L1 TSC offset for svm. I think
tracing the L1 TSC offset is clearer, but then doing it for vmx entailed
either rewriting the function twice, or squashing the refactoring in
this patch.
Paolo
> But I guess it’s a matter of taste…
> Anyway, code looks correct to me. Therefore:
> Reviewed-by: Liran Alon <liran.alon@oracle.com>
>
>> ---
>> Untested still, but throwing it out because it seems pretty
>> obvious...
>>
>> arch/x86/kvm/svm.c | 9 +++++----
>> arch/x86/kvm/vmx.c | 34 +++++++++++++++++-----------------
>> 2 files changed, 22 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index a24733aade4c..0d1a74069a9e 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -1456,10 +1456,11 @@ static u64 svm_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
>> g_tsc_offset = svm->vmcb->control.tsc_offset -
>> svm->nested.hsave->control.tsc_offset;
>> svm->nested.hsave->control.tsc_offset = offset;
>> - } else
>> - trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> - svm->vmcb->control.tsc_offset,
>> - offset);
>> + }
>> +
>> + trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> + svm->vmcb->control.tsc_offset - g_tsc_offset,
>> + offset);
>>
>> svm->vmcb->control.tsc_offset = offset + g_tsc_offset;
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 764c23dc444f..e7d3f7d35355 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -3466,24 +3466,24 @@ static u64 vmx_read_l1_tsc_offset(struct kvm_vcpu *vcpu)
>>
>> static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
>> {
>> - u64 active_offset = offset;
>> - if (is_guest_mode(vcpu)) {
>> - /*
>> - * We're here if L1 chose not to trap WRMSR to TSC. According
>> - * to the spec, this should set L1's TSC; The offset that L1
>> - * set for L2 remains unchanged, and still needs to be added
>> - * to the newly set TSC to get L2's TSC.
>> - */
>> - struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
>> - if (nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING))
>> - active_offset += vmcs12->tsc_offset;
>> - } else {
>> - trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> - vmcs_read64(TSC_OFFSET), offset);
>> - }
>> + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
>> + u64 g_tsc_offset = 0;
>> +
>> + /*
>> + * We're here if L1 chose not to trap WRMSR to TSC. According
>> + * to the spec, this should set L1's TSC; The offset that L1
>> + * set for L2 remains unchanged, and still needs to be added
>> + * to the newly set TSC to get L2's TSC.
>> + */
>> + if (is_guest_mode(vcpu) &&
>> + (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING))
>> + g_tsc_offset = vmcs12->tsc_offset;
>>
>> - vmcs_write64(TSC_OFFSET, active_offset);
>> - return active_offset;
>> + trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> + vcpu->arch.tsc_offset - g_tsc_offset,
>> + offset);
>> + vmcs_write64(TSC_OFFSET, offset + g_tsc_offset);
>> + return offset + g_tsc_offset;
>> }
>>
>> /*
>> --
>> 1.8.3.1
>>
>
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: x86: Trace changes to active TSC offset regardless if vCPU in guest-mode
2018-11-25 21:38 ` Liran Alon
2018-11-26 10:27 ` Paolo Bonzini
@ 2018-11-26 10:27 ` Paolo Bonzini
1 sibling, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2018-11-26 10:27 UTC (permalink / raw)
To: Liran Alon; +Cc: linux-kernel, kvm, Jim Mattson
On 25/11/18 22:38, Liran Alon wrote:
>
>
>> On 25 Nov 2018, at 19:53, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> For some reason, kvm_x86_ops->write_l1_tsc_offset() skipped trace
>> of change to active TSC offset in case vCPU is in guest-mode.
>> This patch changes write_l1_tsc_offset() behavior to trace any change
>> to active TSC offset to aid debugging. The VMX code is changed to
>> look more similar to SVM, which is in my opinion nicer.
>>
>> Based on a patch by Liran Alon.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>
> I would have applied this refactoring change on top of my original version of this patch. Easier to read and review.
Your original version of the patch is a bit different, in that it traced
the L2 TSC offset. I think tracing the L1 TSC offset is clearer, but
then doing it for vmx entailed either rewriting the function twice, or
squashing the refactoring in this patch.
Paolo
> But I guess it’s a matter of taste…
> Anyway, code looks correct to me. Therefore:
> Reviewed-by: Liran Alon <liran.alon@oracle.com>
>
>> ---
>> Untested still, but throwing it out because it seems pretty
>> obvious...
>>
>> arch/x86/kvm/svm.c | 9 +++++----
>> arch/x86/kvm/vmx.c | 34 +++++++++++++++++-----------------
>> 2 files changed, 22 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index a24733aade4c..0d1a74069a9e 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -1456,10 +1456,11 @@ static u64 svm_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
>> g_tsc_offset = svm->vmcb->control.tsc_offset -
>> svm->nested.hsave->control.tsc_offset;
>> svm->nested.hsave->control.tsc_offset = offset;
>> - } else
>> - trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> - svm->vmcb->control.tsc_offset,
>> - offset);
>> + }
>> +
>> + trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> + svm->vmcb->control.tsc_offset - g_tsc_offset,
>> + offset);
>>
>> svm->vmcb->control.tsc_offset = offset + g_tsc_offset;
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 764c23dc444f..e7d3f7d35355 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -3466,24 +3466,24 @@ static u64 vmx_read_l1_tsc_offset(struct kvm_vcpu *vcpu)
>>
>> static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
>> {
>> - u64 active_offset = offset;
>> - if (is_guest_mode(vcpu)) {
>> - /*
>> - * We're here if L1 chose not to trap WRMSR to TSC. According
>> - * to the spec, this should set L1's TSC; The offset that L1
>> - * set for L2 remains unchanged, and still needs to be added
>> - * to the newly set TSC to get L2's TSC.
>> - */
>> - struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
>> - if (nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING))
>> - active_offset += vmcs12->tsc_offset;
>> - } else {
>> - trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> - vmcs_read64(TSC_OFFSET), offset);
>> - }
>> + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
>> + u64 g_tsc_offset = 0;
>> +
>> + /*
>> + * We're here if L1 chose not to trap WRMSR to TSC. According
>> + * to the spec, this should set L1's TSC; The offset that L1
>> + * set for L2 remains unchanged, and still needs to be added
>> + * to the newly set TSC to get L2's TSC.
>> + */
>> + if (is_guest_mode(vcpu) &&
>> + (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING))
>> + g_tsc_offset = vmcs12->tsc_offset;
>>
>> - vmcs_write64(TSC_OFFSET, active_offset);
>> - return active_offset;
>> + trace_kvm_write_tsc_offset(vcpu->vcpu_id,
>> + vcpu->arch.tsc_offset - g_tsc_offset,
>> + offset);
>> + vmcs_write64(TSC_OFFSET, offset + g_tsc_offset);
>> + return offset + g_tsc_offset;
>> }
>>
>> /*
>> --
>> 1.8.3.1
>>
>
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2018-11-25 17:53 [PATCH] KVM: x86: Trace changes to active TSC offset regardless if vCPU in guest-mode Paolo Bonzini
2018-11-25 21:38 ` Liran Alon
2018-11-26 10:27 ` Paolo Bonzini
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