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

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Message-ID: <SN6PR12MB2767168CA61257A85B29C26D8E869@SN6PR12MB2767.namprd12.prod.outlook.com>
Date:   Wed, 17 Feb 2021 14:00:44 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>, "bp@...e.de" <bp@...e.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "srutherford@...gle.com" <srutherford@...gle.com>,
        "venu.busireddy@...cle.com" <venu.busireddy@...cle.com>,
        "Singh, Brijesh" <brijesh.singh@....com>
Subject: RE: [PATCH v10 10/16] KVM: x86: Introduce KVM_GET_SHARED_PAGES_LIST
 ioctl

[AMD Public Use]

-----Original Message-----
From: Sean Christopherson <seanjc@...gle.com> 
Sent: Tuesday, February 16, 2021 7:03 PM
To: Kalra, Ashish <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; Lendacky, Thomas <Thomas.Lendacky@....com>; x86@...nel.org; kvm@...r.kernel.org; linux-kernel@...r.kernel.org; srutherford@...gle.com; venu.busireddy@...cle.com; Singh, Brijesh <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.

What is the advantage of passing KVM_HC_PAGE_ENC_STATUS through to user-space ?

As such it is just a simple interface to get the shared page list via the get/set ioctl's. simply an array is passed to these ioctl to get/set the shared pages
list.

>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?

Even the in-guest migration helper will be using page encryption status hypercalls, so some interface is surely required.

Also the in-guest migration will be mainly an OVMF component, won't  really be a full fledged kernel driver in the guest.

Thanks,
Ashish