linux-kernel - Re: [PATCH 00/19] Refresh queued CET virtualization series

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Message-ID: <62d4f7f0-e7b2-83ad-a2c7-a90153129da2@redhat.com>
Date:   Thu, 16 Jun 2022 12:21:20 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Yang Weijiang <weijiang.yang@...el.com>
Cc:     seanjc@...gle.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, rick.p.edgecombe@...el.com
Subject: Re: [PATCH 00/19] Refresh queued CET virtualization series

On 6/16/22 12:12, Peter Zijlstra wrote:
> Do I understand this right in that a host without X86_KERNEL_IBT cannot
> run a guest with X86_KERNEL_IBT on? That seems unfortunate, since that
> was exactly what I did while developing the X86_KERNEL_IBT patches.
> 
> I'm thinking that if the hardware supports it, KVM should expose it,
> irrespective of the host kernel using it.

For IBT in particular, I think all processor state is only loaded and 
stored at vmentry/vmexit (does not need XSAVES), so it should be feasible.

Paolo