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From: David Hildenbrand <david@redhat.com>
To: jejb@linux.ibm.com, Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm list <kvm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Joerg Roedel <jroedel@suse.de>, Andi Kleen <ak@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Varad Gautam <varad.gautam@suse.com>,
	Dario Faggioli <dfaggioli@suse.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	linux-mm@kvack.org, linux-coco@lists.linux.dev,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	Sathyanarayanan Kuppuswamy
	<sathyanarayanan.kuppuswamy@linux.intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Yu Zhang <yu.c.zhang@linux.intel.com>
Subject: Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory
Date: Wed, 1 Sep 2021 18:22:06 +0200	[thread overview]
Message-ID: <a259e10d-39c9-c4a5-0ab4-f42a1b9bfaee@redhat.com> (raw)
In-Reply-To: <bd22ef54224d15ee89130728c408f70da0516eaa.camel@linux.ibm.com>

On 01.09.21 18:18, James Bottomley wrote:
> On Wed, 2021-09-01 at 08:54 -0700, Andy Lutomirski wrote:
> [...]
>> If you want to swap a page on TDX, you can't.  Sorry, go directly to
>> jail, do not collect $200.
> 
> Actually, even on SEV-ES you can't either.  You can read the encrypted
> page and write it out if you want, but unless you swap it back to the
> exact same physical memory location, the encryption key won't work.
> Since we don't guarantee this for swap, I think swap won't actually
> work for any confidential computing environment.
> 
>> So I think there are literally zero code paths that currently call
>> try_to_unmap() that will actually work like that on TDX.  If we run
>> out of memory on a TDX host, we can kill the guest completely and
>> reclaim all of its memory (which probably also involves killing QEMU
>> or whatever other user program is in charge), but that's really our
>> only option.
> 
> I think our only option for swap is guest co-operation.  We're going to
> have to inflate a balloon or something in the guest and have the guest
> driver do some type of bounce of the page, where it becomes an
> unencrypted page in the guest (so the host can read it without the
> physical address keying of the encryption getting in the way) but
> actually encrypted with a swap transfer key known only to the guest.  I
> assume we can use the page acceptance infrastructure currently being
> discussed elsewhere to do swap back in as well ... the host provides
> the guest with the encrypted swap page and the guest has to decrypt it
> and place it in encrypted guest memory.

Ballooning is indeed *the* mechanism to avoid swapping in the hypervisor 
and much rather let the guest swap. Shame it requires trusting a guest, 
which we, in general, can't. Not to mention other issues we already do 
have with ballooning (latency, broken auto-ballooning, over-inflating, ...).

-- 
Thanks,

David / dhildenb


  reply	other threads:[~2021-09-01 16:22 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-24  0:52 [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory Sean Christopherson
2021-08-24 10:48 ` Yu Zhang
2021-08-26  0:35   ` Sean Christopherson
2021-08-26 13:23     ` Yu Zhang
2021-08-26 10:15 ` David Hildenbrand
2021-08-26 17:05   ` Andy Lutomirski
2021-08-26 21:26     ` David Hildenbrand
2021-08-27 18:24       ` Andy Lutomirski
2021-08-27 22:28         ` Sean Christopherson
2021-08-31 19:12           ` David Hildenbrand
2021-08-31 20:45             ` Sean Christopherson
2021-09-01  7:51               ` David Hildenbrand
2021-08-27  2:31   ` Yu Zhang
2021-08-31 19:08     ` David Hildenbrand
2021-08-31 20:01       ` Andi Kleen
2021-08-31 20:15         ` David Hildenbrand
2021-08-31 20:39           ` Andi Kleen
2021-09-01  3:34             ` Yu Zhang
2021-09-01  4:53     ` Andy Lutomirski
2021-09-01  7:12       ` Tian, Kevin
2021-09-01 10:24       ` Yu Zhang
2021-09-01 16:07         ` Andy Lutomirski
2021-09-01 16:27           ` David Hildenbrand
2021-09-02  8:34             ` Yu Zhang
2021-09-02  8:44               ` David Hildenbrand
2021-09-02 11:02                 ` Yu Zhang
2021-09-02  8:19           ` Yu Zhang
2021-09-02 18:41             ` Andy Lutomirski
2021-09-07  1:33             ` Yan Zhao
2021-09-02  9:27           ` Joerg Roedel
2021-09-02 18:41             ` Andy Lutomirski
2021-09-02 18:57               ` Sean Christopherson
2021-09-02 19:07                 ` Dave Hansen
2021-09-02 20:42                   ` Andy Lutomirski
2021-08-27 22:18   ` Sean Christopherson
2021-08-31 19:07     ` David Hildenbrand
2021-08-31 21:54       ` Sean Christopherson
2021-09-01  8:09         ` David Hildenbrand
2021-09-01 15:54           ` Andy Lutomirski
2021-09-01 16:16             ` David Hildenbrand
2021-09-01 17:09               ` Andy Lutomirski
2021-09-01 16:18             ` James Bottomley
2021-09-01 16:22               ` David Hildenbrand [this message]
2021-09-01 16:31                 ` James Bottomley
2021-09-01 16:37                   ` David Hildenbrand
2021-09-01 16:45                     ` James Bottomley
2021-09-01 17:08                       ` David Hildenbrand
2021-09-01 17:50                         ` Sean Christopherson
2021-09-01 17:53                           ` David Hildenbrand
2021-09-01 17:08               ` Andy Lutomirski
2021-09-01 17:13                 ` James Bottomley
2021-09-02 10:18                 ` Joerg Roedel
2021-09-01 18:24               ` Andy Lutomirski
2021-09-01 19:26               ` Dave Hansen
2021-09-07 15:00               ` Tom Lendacky
2021-09-01  4:58       ` Andy Lutomirski
2021-09-01  7:49         ` David Hildenbrand
2021-09-02 18:47 ` Kirill A. Shutemov
2021-09-02 20:33   ` Sean Christopherson
2021-09-03 19:14     ` Kirill A. Shutemov
2021-09-03 19:15       ` Andy Lutomirski
2021-09-10 17:18         ` Kirill A. Shutemov
2021-09-15 19:58           ` Chao Peng
2021-09-15 13:51             ` David Hildenbrand
2021-09-15 14:29               ` Kirill A. Shutemov
2021-09-15 14:59                 ` David Hildenbrand
2021-09-15 15:35                   ` David Hildenbrand
2021-09-15 20:04                   ` Kirill A. Shutemov
2021-09-15 14:11             ` Kirill A. Shutemov
2021-09-16  7:36               ` Chao Peng
2021-09-16  9:24               ` Paolo Bonzini

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