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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <SN6PR12MB2767A978C3A2B43982F2F4898E859@SN6PR12MB2767.namprd12.prod.outlook.com>
Date:   Thu, 18 Feb 2021 17:05:23 +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: Thursday, February 18, 2021 10:39 AM
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 18, 2021, Kalra, Ashish wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> On Wed, Feb 17, 2021, Kalra, Ashish wrote:
> >> From: Sean Christopherson <seanjc@...gle.com> 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.
>> 
>> > It eliminates any probability of the kernel choosing the wrong data 
>> > structure, and it's two fewer ioctls to maintain and test.
>> 
>> The set shared pages list ioctl cannot be avoided as it needs to be 
>> issued to setup the shared pages list on the migrated VM, it cannot be 
>> achieved by passing KVM_HC_PAGE_ENC_STATUS through to user-space.

>Why's that?  AIUI, KVM doesn't do anything with the list other than pass it back to userspace.  Assuming that's the case, userspace can just hold onto the list >for the next migration.

KVM does use it as part of the SEV DBG_DECTYPT API, within sev_dbg_decrypt() to check if the guest page(s) are encrypted or not,
and accordingly use it to decide whether to decrypt the guest page(s) and return that back to user-space or just return it as it is.

Thanks,
Ashish