linux-kernel - Re: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V

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Message-ID: <87ilp2i2oi.fsf@redhat.com>
Date:   Wed, 15 Jun 2022 13:30:53 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     mail@...rudhrb.com, kumarpraveen@...ux.microsoft.com,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        wei.liu@...nel.org, robert.bradford@...el.com, liuwe@...rosoft.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Ilias Stamatis <ilstam@...zon.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V

Vitaly Kuznetsov <vkuznets@...hat.com> writes:

> Vitaly Kuznetsov <vkuznets@...hat.com> writes:
>
>> Anirudh Rayabharam <anrayabh@...ux.microsoft.com> writes:
>>
>> ...
>>
>>>
>>> As per the comments in arch/x86/kvm/vmx/evmcs.h, TSC multiplier field is
>>> currently not supported in EVMCS.
>>
>> The latest version:
>> https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/datatypes/hv_vmx_enlightened_vmcs
>>
>> has it, actually. It was missing before (compare with e.g. 6.0b version
>> here:
>> https://github.com/MicrosoftDocs/Virtualization-Documentation/raw/live/tlfs/Hypervisor%20Top%20Level%20Functional%20Specification%20v6.0b.pdf)
>>
>> but AFAIR TSC scaling wasn't advertised by genuine Hyper-V either.
>> Interestingly enough, eVMCS version didn't change when these fields were
>> added, it is still '1'.
>>
>> I even have a patch in my stash (attached). I didn't send it out because
>> it wasn't properly tested with different Hyper-V versions.
>
> And of course I forgot a pre-requisite patch which updates 'struct
> hv_enlightened_vmcs' to the latest:
>

The good news is that TscMultiplies seems to work fine for me, at least
with an Azure Dv5 instance where I can see Tsc scaling exposed. The bad
news is that a few more patches are needed:

1) Fix 'struct hv_enlightened_vmcs' definition:
https://lore.kernel.org/kvm/20220613133922.2875594-20-vkuznets@redhat.com/

2) Define VMCS-to-EVMCS conversion for the new fields :

diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index 6a61b1ae7942..707a8de11802 100644
--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -28,6 +28,8 @@ const struct evmcs_field vmcs_field_to_evmcs_1[] = {
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_HOST_GRP1),
        EVMCS1_FIELD(HOST_IA32_EFER, host_ia32_efer,
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_HOST_GRP1),
+       EVMCS1_FIELD(HOST_IA32_PERF_GLOBAL_CTRL, host_ia32_perf_global_ctrl,
+                    HV_VMX_ENLIGHTENED_CLEAN_FIELD_HOST_GRP1),
        EVMCS1_FIELD(HOST_CR0, host_cr0,
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_HOST_GRP1),
        EVMCS1_FIELD(HOST_CR3, host_cr3,
@@ -78,6 +80,8 @@ const struct evmcs_field vmcs_field_to_evmcs_1[] = {
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1),
        EVMCS1_FIELD(GUEST_IA32_EFER, guest_ia32_efer,
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1),
+       EVMCS1_FIELD(GUEST_IA32_PERF_GLOBAL_CTRL, guest_ia32_perf_global_ctrl,
+                    HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1),
        EVMCS1_FIELD(GUEST_PDPTR0, guest_pdptr0,
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1),
        EVMCS1_FIELD(GUEST_PDPTR1, guest_pdptr1,
@@ -126,24 +130,47 @@ const struct evmcs_field vmcs_field_to_evmcs_1[] = {
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1),
        EVMCS1_FIELD(XSS_EXIT_BITMAP, xss_exit_bitmap,
                     HV_VMX_ENLIGHTENED_CLEAN_FIELD_CONTROL_GRP2),
+       EVMCS1_FIELD(ENCLS_EXITING_BITMAP, encls_exiting_bitmap,
+                    HV_VMX_ENLIGHTENED_CLEAN_FIELD_CONTROL_GRP2),
+       EVMCS1_FIELD(TSC_MULTIPLIER, tsc_multiplier,
+                    HV_VMX_ENLIGHTENED_CLEAN_FIELD_CONTROL_GRP2),

...

so it is becoming more and more complicated to assemble for testing. Let
me finish my testing and I'll put a series together and send it out to
simplify the process. Stay tuned!

-- 
Vitaly