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From: Paolo Bonzini <pbonzini@redhat.com>
To: "Stamatis, Ilias" <ilstam@amazon.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"ilstam@mailbox.org" <ilstam@mailbox.org>
Cc: "jmattson@google.com" <jmattson@google.com>,
	"Woodhouse, David" <dwmw@amazon.co.uk>,
	"vkuznets@redhat.com" <vkuznets@redhat.com>,
	"haozhong.zhang@intel.com" <haozhong.zhang@intel.com>,
	"joro@8bytes.org" <joro@8bytes.org>,
	"mtosatti@redhat.com" <mtosatti@redhat.com>,
	"zamsden@gmail.com" <zamsden@gmail.com>,
	"seanjc@google.com" <seanjc@google.com>,
	"dplotnikov@virtuozzo.com" <dplotnikov@virtuozzo.com>,
	"wanpengli@tencent.com" <wanpengli@tencent.com>
Subject: Re: [PATCH 4/8] KVM: VMX: Adjust the TSC-related VMCS fields on L2 entry and exit
Date: Mon, 10 May 2021 16:11:50 +0200	[thread overview]
Message-ID: <9506c826-face-e816-d88a-3797872f26d2@redhat.com> (raw)
In-Reply-To: <8ebf2b17f339bf21b69bba41575e62f98ec87105.camel@amazon.com>

On 06/05/21 19:35, Stamatis, Ilias wrote:
> On Thu, 2021-05-06 at 13:32 +0200, Paolo Bonzini wrote:
>> On 06/05/21 12:32, ilstam@mailbox.org wrote:
>>> +     if (vmcs12->cpu_based_vm_exec_control &
>>> CPU_BASED_USE_TSC_OFFSETTING) {
>>> +             if (vmcs12->secondary_vm_exec_control &
>>> SECONDARY_EXEC_TSC_SCALING) {
>>> +                     vcpu->arch.tsc_offset =
>>> kvm_compute_02_tsc_offset(
>>> +                                     vcpu->arch.l1_tsc_offset,
>>> +                                     vmcs12->tsc_multiplier,
>>> +                                     vmcs12->tsc_offset);
>>> +
>>> +                     vcpu->arch.tsc_scaling_ratio =
>>> mul_u64_u64_shr(
>>> +                                     vcpu->arch.tsc_scaling_ratio,
>>> +                                     vmcs12->tsc_multiplier,
>>> +                                     kvm_tsc_scaling_ratio_frac_bit
>>> s);
>>> +             } else {
>>> +                     vcpu->arch.tsc_offset += vmcs12->tsc_offset;
>>> +             }
>>
>> The computation of vcpu->arch.tsc_offset is (not coincidentially) the
>> same that appears in patch 6
>>
>> +           (vmcs12->cpu_based_vm_exec_control &
>> CPU_BASED_USE_TSC_OFFSETTING)) {
>> +               if (vmcs12->secondary_vm_exec_control &
>> SECONDARY_EXEC_TSC_SCALING) {
>> +                       cur_offset = kvm_compute_02_tsc_offset(
>> +                                       l1_offset,
>> +                                       vmcs12->tsc_multiplier,
>> +                                       vmcs12->tsc_offset);
>> +               } else {
>> +                       cur_offset = l1_offset + vmcs12->tsc_offset;
>>
>> So I think you should just pass vmcs12 and the L1 offset to
>> kvm_compute_02_tsc_offset, and let it handle both cases (and possibly
>> even set vcpu->arch.tsc_scaling_ratio in the same function).
> 
> That was my thinking initially too. However, kvm_compute_02_tsc_offset
> is defined in x86.c which is vmx-agnostic and hence 'struct vmcs12' is
> not defined there.

Good point.  Yeah, it's trading one comde duplication for another. 
Right now there's already code duplication in write_l1_tsc_offset, so it 
makes some sense to limit duplication _within_ the file and lose in 
duplicated code across vmx/svm, but either is okay.

Paolo


  reply	other threads:[~2021-05-10 14:16 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-06 10:32 [PATCH 0/8] KVM: VMX: Implement nested TSC scaling ilstam
2021-05-06 10:32 ` [PATCH 1/8] KVM: VMX: Add a TSC multiplier field in VMCS12 ilstam
2021-05-06 14:50   ` kernel test robot
2021-05-06 17:36   ` Jim Mattson
2021-05-10 13:42   ` Maxim Levitsky
2021-05-06 10:32 ` [PATCH 2/8] KVM: X86: Store L1's TSC scaling ratio in 'struct kvm_vcpu_arch' ilstam
2021-05-10 13:43   ` Maxim Levitsky
2021-05-06 10:32 ` [PATCH 3/8] KVM: X86: Pass an additional 'L1' argument to kvm_scale_tsc() ilstam
2021-05-10 13:52   ` Maxim Levitsky
2021-05-10 15:44     ` Stamatis, Ilias
2021-05-06 10:32 ` [PATCH 4/8] KVM: VMX: Adjust the TSC-related VMCS fields on L2 entry and exit ilstam
2021-05-06 11:32   ` Paolo Bonzini
2021-05-06 17:35     ` Stamatis, Ilias
2021-05-10 14:11       ` Paolo Bonzini [this message]
2021-05-10 13:53   ` Maxim Levitsky
2021-05-10 14:44     ` Stamatis, Ilias
2021-05-11 12:38       ` Maxim Levitsky
2021-05-11 15:11         ` Stamatis, Ilias
2021-05-06 10:32 ` [PATCH 5/8] KVM: X86: Move tracing outside write_l1_tsc_offset() ilstam
2021-05-10 13:54   ` Maxim Levitsky
2021-05-06 10:32 ` [PATCH 6/8] KVM: VMX: Make vmx_write_l1_tsc_offset() work with nested TSC scaling ilstam
2021-05-10 13:54   ` Maxim Levitsky
2021-05-10 16:08     ` Stamatis, Ilias
2021-05-11 12:44       ` Maxim Levitsky
2021-05-11 17:44         ` Stamatis, Ilias
2021-05-06 10:32 ` [PATCH 7/8] KVM: VMX: Expose TSC scaling to L2 ilstam
2021-05-10 13:56   ` Maxim Levitsky
2021-05-06 10:32 ` [PATCH 8/8] KVM: selftests: x86: Add vmx_nested_tsc_scaling_test ilstam
2021-05-10 13:59   ` Maxim Levitsky
2021-05-11 11:16     ` Stamatis, Ilias
2021-05-11 12:47       ` Maxim Levitsky
2021-05-11 14:02         ` Stamatis, Ilias
2021-05-06 17:16 ` [PATCH 0/8] KVM: VMX: Implement nested TSC scaling Jim Mattson
2021-05-06 17:48   ` Stamatis, Ilias
2021-05-10 13:43     ` Maxim Levitsky
2021-05-10 14:29   ` Paolo Bonzini

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