linux-kernel - Re: [PATCH 0/3] x86/kvm/hyper-v: fix enlightened VMCS & QEMU4.2

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Message-ID: <adbf1ea0-9c59-f683-ce03-a8fd92bfe488@redhat.com>
Date:   Wed, 5 Feb 2020 15:55:34 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, Liran Alon <liran.alon@...cle.com>,
        Roman Kagan <rkagan@...tuozzo.com>
Subject: Re: [PATCH 0/3] x86/kvm/hyper-v: fix enlightened VMCS & QEMU4.2

On 05/02/20 13:30, Vitaly Kuznetsov wrote:
> With fine grained VMX feature enablement QEMU>=4.2 tries to do KVM_SET_MSRS
> with default (matching CPU model) values and in case eVMCS is also enabled,
> fails. While the regression is in QEMU, it may still be preferable to
> fix this in KVM.
> 
> It would be great if we could just omit the VMX feature filtering in KVM
> and make this guest's responsibility: if it switches to using enlightened
> vmcs it should be aware that not all hardware features are going to be
> supported. Genuine Hyper-V, however, fails the test. It, for example,
> enables SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES and without
> 'apic_access_addr' field in eVMCS there's not much we can do in KVM.
> Microsoft confirms the bug but it is unclear if it will ever get fixed
> in the existing Hyper-V versions as genuine Hyper-V never exposes
> these unsupported controls to L1.
> 
> Changes since 'RFC':
> - Go with the bare minimum [Paolo]
> 
> KVM RFC:
> https://lore.kernel.org/kvm/20200115171014.56405-1-vkuznets@redhat.com/
> 
> QEMU RFC@:
> https://lists.nongnu.org/archive/html/qemu-devel/2020-01/msg00123.html
> 
> Vitaly Kuznetsov (3):
>   x86/kvm/hyper-v: remove stale evmcs_already_enabled check from
>     nested_enable_evmcs()
>   x86/kvm/hyper-v: move VMX controls sanitization out of
>     nested_enable_evmcs()
>   x86/kvm/hyper-v: don't allow to turn on unsupported VMX controls for
>     nested guests
> 
>  arch/x86/kvm/vmx/evmcs.c  | 90 ++++++++++++++++++++++++++++++++++-----
>  arch/x86/kvm/vmx/evmcs.h  |  3 ++
>  arch/x86/kvm/vmx/nested.c |  3 ++
>  arch/x86/kvm/vmx/vmx.c    | 16 ++++++-
>  4 files changed, 99 insertions(+), 13 deletions(-)
> 

Queued, thanks.

Paolo