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From: "Stamatis, Ilias" <ilstam@amazon.com>
To: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"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: Thu, 6 May 2021 17:35:47 +0000	[thread overview]
Message-ID: <8ebf2b17f339bf21b69bba41575e62f98ec87105.camel@amazon.com> (raw)
In-Reply-To: <50f86951-1cea-b7aa-7236-f28edd5eca8d@redhat.com>

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).
> 
> Paolo
> 

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. 

The way it is now, that function can be re-used by svm code in case we
add amd support later.

I could try to define a wrapper in vmx.c instead, that calls
kvm_compute_02_tsc_offset and move all the code there. However, I think
this requires many more changes to the vmx and svm write_l1_tsc_offset
functions and to their caller. I am looking at it now. 

Ilias

  reply	other threads:[~2021-05-06 17:36 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 [this message]
2021-05-10 14:11       ` Paolo Bonzini
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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