linux-kernel - Re: [PATCH v10 10/16] KVM: x86: Introduce KVM_GET_SHARED_PAGES

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Date:   Tue, 16 Feb 2021 17:03:19 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, rkrcmar@...hat.com, joro@...tes.org, bp@...e.de,
        thomas.lendacky@....com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, srutherford@...gle.com,
        venu.busireddy@...cle.com, brijesh.singh@....com
Subject: Re: [PATCH v10 10/16] KVM: x86: Introduce KVM_GET_SHARED_PAGES_LIST
 ioctl

On Thu, Feb 04, 2021, Ashish Kalra wrote:
> From: Brijesh Singh <brijesh.singh@....com>
> 
> The ioctl is used to retrieve a guest's shared pages list.

What's the performance hit to boot time if KVM_HC_PAGE_ENC_STATUS is passed
through to userspace?  That way, userspace could manage the set of pages in
whatever data structure they want, and these get/set ioctls go away.

Also, aren't there plans for an in-guest migration helper?  If so, do we have
any idea what that interface will look like?  E.g. if we're going to end up with
a full fledged driver in the guest, why not bite the bullet now and bypass KVM
entirely?