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SubjectRE: [PATCH v10 10/16] KVM: x86: Introduce KVM_GET_SHARED_PAGES_LIST ioctl
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-----Original Message-----
From: Sean Christopherson <seanjc@google.com>
Sent: Tuesday, February 16, 2021 7:03 PM
To: Kalra, Ashish <Ashish.Kalra@amd.com>
Cc: pbonzini@redhat.com; tglx@linutronix.de; mingo@redhat.com; hpa@zytor.com; rkrcmar@redhat.com; joro@8bytes.org; bp@suse.de; Lendacky, Thomas <Thomas.Lendacky@amd.com>; x86@kernel.org; kvm@vger.kernel.org; linux-kernel@vger.kernel.org; srutherford@google.com; venu.busireddy@oracle.com; Singh, Brijesh <brijesh.singh@amd.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@amd.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

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