RE: [PATCH v10 10/16] KVM: x86: Introduce KVM_GET_SHARED_PAGES_LIST ioctl

[Kalra, Ashish]

[AMD Public Use]

-----Original Message-----
From: Sean Christopherson <seanjc@xxxxxxxxxx> 
Sent: Tuesday, February 16, 2021 7:03 PM
To: Kalra, Ashish <Ashish.Kalra@xxxxxxx>
Cc: pbonzini@xxxxxxxxxx; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx; rkrcmar@xxxxxxxxxx; joro@xxxxxxxxxx; bp@xxxxxxx; Lendacky, Thomas <Thomas.Lendacky@xxxxxxx>; x86@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; srutherford@xxxxxxxxxx; venu.busireddy@xxxxxxxxxx; Singh, Brijesh <brijesh.singh@xxxxxxx>
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@xxxxxxx>
> 
> 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