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Subject: Re: [PATCH] KVM: VMX: enable nested virtualization by default
From:   Liran Alon <liran.alon@oracle.com>
In-Reply-To: <20181016225522.13077-1-pbonzini@redhat.com>
Date:   Wed, 17 Oct 2018 02:13:15 +0300
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        jmattson@google.com
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Message-Id: <1CB58AE6-8057-4D76-8EA5-C219326F3432@oracle.com>
References: <20181016225522.13077-1-pbonzini@redhat.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On 17 Oct 2018, at 1:55, Paolo Bonzini <pbonzini@redhat.com> wrote:
>=20
> With live migration support and finally a good solution for CR2/DR6
> exception payloads, nested VMX should finally be ready for having a =
stable

And good solution for setting/getting vCPU events from userspace with =
correct pending/injected state.

> userspace ABI.  The results of syzkaller fuzzing are not perfect but =
not
> horrible either (and might be partially due to running on GCE, so that
> effectively we're testing three-level nesting on a fork of upstream =
KVM!).
> Enabling it by default seems like a nice way to conclude the 4.20
> pull request. :)
>=20
> Unfortunately, enabling nested SVM in 2009 was a bit premature.  =
However,

Don=E2=80=99t you wish to mention commit which enabled it?

> until live migration support is in place we can reasonably expect that
> it does not offer much in terms of ABI guarantees.  Therefore we are
> still in time to break things and conform as much as possible to the
> interface used for VMX.
>=20
> Suggested-by: Jim Mattson <jmattson@google.com>
> Suggested-by: Liran Alon <liran.alon@oracle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/vmx.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index e665aa7167cf..89fc2a744d7f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -107,7 +107,7 @@ module_param_named(enable_shadow_vmcs, =
enable_shadow_vmcs, bool, S_IRUGO);
>  * VMX and be a hypervisor for its own guests. If nested=3D0, guests =
may not
>  * use VMX instructions.
>  */
> -static bool __read_mostly nested =3D 0;
> +static bool __read_mostly nested =3D 1;
> module_param(nested, bool, S_IRUGO);
>=20
> static u64 __read_mostly host_xss;
> --=20
> 2.17.1
>=20

Woohoo! :)
Reviewed-by: Liran Alon <liran.alon@oracle.com>