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Subject: Re: [PATCH v6 2/5] KVM: x86: Add IBPB support
To:     Wanpeng Li <kernellwp@gmail.com>,
        KarimAllah Ahmed <karahmed@amazon.de>
Cc:     kvm <kvm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        David Woodhouse <dwmw@amazon.co.uk>
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From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Thu, 3 May 2018 11:19:51 +0200
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On 03/05/2018 03:27, Wanpeng Li wrote:
> So for 1) guest->guest attacks 2) guest/ring3->host/ring3 attacks 3)
> guest/ring0->host/ring0 attacks, if IBPB is enough to protect these
> three scenarios and retpoline is not needed?

In theory yes, in practice if you want to do that IBPB is much more
expensive than retpolines, because you'd need an IBPB on vmexit or a
cache flush on vmentry.

Paolo