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From: Paolo Bonzini <pbonzini@redhat.com>
To: Jim Mattson <jmattson@google.com>, ilstam@mailbox.org
Cc: kvm list <kvm@vger.kernel.org>,
	ilstam@amazon.com, Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Joerg Roedel <joro@8bytes.org>,
	Haozhong Zhang <haozhong.zhang@intel.com>,
	zamsden@gmail.com, mtosatti@redhat.com,
	Denis Plotnikov <dplotnikov@virtuozzo.com>,
	David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [PATCH 0/8] KVM: VMX: Implement nested TSC scaling
Date: Mon, 10 May 2021 16:29:40 +0200	[thread overview]
Message-ID: <bdfb8be8-7584-c60b-635e-3595fe481a60@redhat.com> (raw)
In-Reply-To: <CALMp9eSNHf=vmqeer+ZkRa3NhJoLMbEO+OZJaG9qf+2+TQ2grA@mail.gmail.com>

On 06/05/21 19:16, Jim Mattson wrote:
> On Thu, May 6, 2021 at 3:34 AM <ilstam@mailbox.org> wrote:
>>
>> From: Ilias Stamatis <ilstam@amazon.com>
>>
>> KVM currently supports hardware-assisted TSC scaling but only for L1 and it
>> doesn't expose the feature to nested guests. This patch series adds support for
>> nested TSC scaling and allows both L1 and L2 to be scaled with different
>> scaling factors.
>>
>> When scaling and offsetting is applied, the TSC for the guest is calculated as:
>>
>> (TSC * multiplier >> 48) + offset
>>
>> With nested scaling the values in VMCS01 and VMCS12 need to be merged
>> together and stored in VMCS02.
>>
>> The VMCS02 values are calculated as follows:
>>
>> offset_02 = ((offset_01 * mult_12) >> 48) + offset_12
>> mult_02 = (mult_01 * mult_12) >> 48
>>
>> The last patch of the series adds a KVM selftest.
> 
> Will you be doing the same for SVM? The last time I tried to add a
> nested virtualization feature for Intel only, Paolo rapped my knuckles
> with a ruler.

For bugfixes definitely, for features it is definitely nice.

And these days we even have similar-enough code between nVMX and nSVM 
code, that in many cases there's really no good excuse not to do it.

Paolo


      parent reply	other threads:[~2021-05-10 14:32 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
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 [this message]

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