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

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Message-ID: <87pmjbi90m.fsf@redhat.com>
Date:   Tue, 14 Jun 2022 17:01:45 +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:

> 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:

diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
index 0a9407dc0859..038e5ef9b4a6 100644
--- a/arch/x86/include/asm/hyperv-tlfs.h
+++ b/arch/x86/include/asm/hyperv-tlfs.h
@@ -559,9 +559,20 @@ struct hv_enlightened_vmcs {
        u64 partition_assist_page;
        u64 padding64_4[4];
        u64 guest_bndcfgs;
-       u64 padding64_5[7];
+       u64 guest_ia32_perf_global_ctrl;
+       u64 guest_ia32_s_cet;
+       u64 guest_ssp;
+       u64 guest_ia32_int_ssp_table_addr;
+       u64 guest_ia32_lbr_ctl;
+       u64 padding64_5[2];
        u64 xss_exit_bitmap;
-       u64 padding64_6[7];
+       u64 host_ia32_perf_global_ctrl;
+       u64 encls_exiting_bitmap;
+       u64 tsc_multiplier;
+       u64 host_ia32_s_cet;
+       u64 host_ssp;
+       u64 host_ia32_int_ssp_table_addr;
+       u64 padding64_6;
 } __packed;
 
 #define HV_VMX_ENLIGHTENED_CLEAN_FIELD_NONE                    0

-- 
Vitaly