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

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Date:   Thu, 18 Feb 2021 18:32:47 +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.

I will be more concerned about performance hit during guest DMA I/O if the page encryption status hypercalls are passed through to user-space, 
a lot of guest DMA I/O dynamically sets up pages for encryption and then flips them at DMA completion, so guest I/O will surely take a performance 
hit with this pass-through stuff.

Thanks,
Ashish