linux-kernel - Re: [PATCH v10 20/39] KVM: nVMX: hyper-v: Enable L2 TLB flush

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Date:   Wed, 21 Sep 2022 21:24:35 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 20/39] KVM: nVMX: hyper-v: Enable L2 TLB flush

On Wed, Sep 21, 2022, Vitaly Kuznetsov wrote:
> diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
> index 7ad56fbc4b4d..dd1589336e79 100644
> --- a/arch/x86/kvm/vmx/evmcs.h
> +++ b/arch/x86/kvm/vmx/evmcs.h
> @@ -63,6 +63,15 @@ DECLARE_STATIC_KEY_FALSE(enable_evmcs);
>  #define EVMCS1_UNSUPPORTED_VMENTRY_CTRL (0)
>  #define EVMCS1_UNSUPPORTED_VMFUNC (VMX_VMFUNC_EPTP_SWITCHING)
>  
> +/*
> + * Note, Hyper-V isn't actually stealing bit 28 from Intel, just abusing it by
> + * pairing it with architecturally impossible exit reasons.  Bit 28 is set only
> + * on SMI exits to a SMI transfer monitor (STM) and if and only if a MTF VM-Exit
> + * is pending.  I.e. it will never be set by hardware for non-SMI exits (there
> + * are only three), nor will it ever be set unless the VMM is an STM.
> + */
> +#define HV_VMX_SYNTHETIC_EXIT_REASON_TRAP_AFTER_FLUSH 0x10000031

This definition should go into hyperv-tlfs.h since it's take verbatim from the TLFS.

https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/nested-virtualization#synthetic-vm-exit