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Message-ID: <YqgU2KfFCqawbTkW@anrayabh-desk>
Date: Tue, 14 Jun 2022 10:25:52 +0530
From: Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
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>, mail@...rudhrb.com,
kumarpraveen@...ux.microsoft.com, wei.liu@...nel.org,
robert.bradford@...el.com, liuwe@...rosoft.com,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Don't expose TSC scaling to L1 when on Hyper-V
On Mon, Jun 13, 2022 at 06:49:17PM +0200, Paolo Bonzini wrote:
> On 6/13/22 18:16, Anirudh Rayabharam wrote:
> > + if (!kvm_has_tsc_control)
> > + msrs->secondary_ctls_high &= ~SECONDARY_EXEC_TSC_SCALING;
> > +
> > msrs->secondary_ctls_low = 0;
> > msrs->secondary_ctls_high &=
> > SECONDARY_EXEC_DESC |
> > @@ -6667,8 +6670,7 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
> > SECONDARY_EXEC_RDRAND_EXITING |
> > SECONDARY_EXEC_ENABLE_INVPCID |
> > SECONDARY_EXEC_RDSEED_EXITING |
> > - SECONDARY_EXEC_XSAVES |
> > - SECONDARY_EXEC_TSC_SCALING;
> > + SECONDARY_EXEC_XSAVES;
> > /*
>
> This is wrong because it _always_ disables SECONDARY_EXEC_TSC_SCALING,
> even if kvm_has_tsc_control == true.
The MSR actually allows 1-setting of the "use TSC scaling" control. So this
line is redundant anyway.
>
> That said, I think a better implementation of this patch is to just add
> a version of evmcs_sanitize_exec_ctrls that takes a struct
> nested_vmx_msrs *, and call it at the end of nested_vmx_setup_ctl_msrs like
>
> evmcs_sanitize_nested_vmx_vsrs(msrs);
Sanitize at the end might not work because I see some cases in
nested_vmx_setup_ctls_msrs() where we want to expose some things to L1
even though the hardware doesn't support it.
>
> Even better (but I cannot "mentally test it" offhand) would be just
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index e802f71a9e8d..b3425ce835c5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1862,7 +1862,7 @@ int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> * sanity checking and refuse to boot. Filter all unsupported
> * features out.
> */
> - if (!msr_info->host_initiated &&
> + if (static_branch_unlikely(&enable_evmcs) ||
> vmx->nested.enlightened_vmcs_enabled)
> nested_evmcs_filter_control_msr(msr_info->index,
> &msr_info->data);
I will try this.
Thanks,
Anirudh.
>
> I cannot quite understand the host_initiated check, so I'll defer to
> Vitaly on why it is needed. Most likely, removing it would cause some
> warnings in QEMU with e.g. "-cpu Haswell,+vmx"; but I think it's a
> userspace bug and we should remove that part of the condition. You
> don't need to worry about that part, we'll cross that bridge if the
> above patch works for your case.
>
> Thanks,
>
> Paolo
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