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Subject: Re: [FYI PATCH 0/7] Mitigation for CVE-2018-12207
To:     Jinpu Wang <jinpuwang@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "KVM-ML (kvm@vger.kernel.org)" <kvm@vger.kernel.org>
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From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Wed, 13 Nov 2019 15:44:08 +0100
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On 13/11/19 14:00, Jinpu Wang wrote:
> Hi Paolo, hi list,
>=20
> Thanks for info, do we need qemu patch for full mitigation?
> Debian mentioned:
> https://linuxsecurity.com/advisories/debian/debian-dsa-4566-1-qemu-securi=
ty-update-17-10-10
> "
>     A qemu update adding support for the PSCHANGE_MC_NO feature, which
>     allows to disable iTLB Multihit mitigations in nested hypervisors
>     will be provided via DSA 4566-1.
>=20
> "
> But It's not yet available  publicly.

I will send it today, but it's not needed for full mitigation.  It just
provides a knob to turn it on and off in nested hypervisors.

> About the performance hit, do you know any number? probably the answer
> is workload dependent.

We generally measured 0-4%.  There can be latency spikes for RT, which I
will send a patch for soon.

Paolo