From: David Hildenbrand <david@redhat.com>
To: Yu Zhang <yu.c.zhang@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>,
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@vger.kernel.org, linux-kernel@vger.kernel.org,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
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 <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Varad Gautam <varad.gautam@suse.com>,
Dario Faggioli <dfaggioli@suse.com>,
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>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>
Subject: Re: [RFC] KVM: mm: fd-based approach for supporting KVM guest private memory
Date: Tue, 31 Aug 2021 21:08:33 +0200 [thread overview]
Message-ID: <243bc6a3-b43b-cd18-9cbb-1f42a5de802f@redhat.com> (raw)
In-Reply-To: <20210827023150.jotwvom7mlsawjh4@linux.intel.com>
On 27.08.21 04:31, Yu Zhang wrote:
> On Thu, Aug 26, 2021 at 12:15:48PM +0200, David Hildenbrand wrote:
>> On 24.08.21 02:52, Sean Christopherson wrote:
>>> The goal of this RFC is to try and align KVM, mm, and anyone else with skin in the
>>> game, on an acceptable direction for supporting guest private memory, e.g. for
>>> Intel's TDX. The TDX architectural effectively allows KVM guests to crash the
>>> host if guest private memory is accessible to host userspace, and thus does not
>>> play nice with KVM's existing approach of pulling the pfn and mapping level from
>>> the host page tables.
>>>
>>> This is by no means a complete patch; it's a rough sketch of the KVM changes that
>>> would be needed. The kernel side of things is completely omitted from the patch;
>>> the design concept is below.
>>>
>>> There's also fair bit of hand waving on implementation details that shouldn't
>>> fundamentally change the overall ABI, e.g. how the backing store will ensure
>>> there are no mappings when "converting" to guest private.
>>>
>>
>> This is a lot of complexity and rather advanced approaches (not saying they
>> are bad, just that we try to teach the whole stack something completely
>> new).
>>
>>
>> What I think would really help is a list of requirements, such that
>> everybody is aware of what we actually want to achieve. Let me start:
>>
>> GFN: Guest Frame Number
>> EPFN: Encrypted Physical Frame Number
>>
>>
>> 1) An EPFN must not get mapped into more than one VM: it belongs exactly to
>> one VM. It must neither be shared between VMs between processes nor between
>> VMs within a processes.
>>
>>
>> 2) User space (well, and actually the kernel) must never access an EPFN:
>>
>> - If we go for an fd, essentially all operations (read/write) have to
>> fail.
>> - If we have to map an EPFN into user space page tables (e.g., to
>> simplify KVM), we could only allow fake swap entries such that "there
>> is something" but it cannot be accessed and is flagged accordingly.
>> - /proc/kcore and friends have to be careful as well and should not read
>> this memory. So there has to be a way to flag these pages.
>>
>> 3) We need a way to express the GFN<->EPFN mapping and essentially assign an
>> EPFN to a GFN.
>>
>>
>> 4) Once we assigned a EPFN to a GFN, that assignment must not longer change.
>> Further, an EPFN must not get assigned to multiple GFNs.
>>
>>
>> 5) There has to be a way to "replace" encrypted parts by "shared" parts
>> and the other way around.
>>
>> What else?
>
> Thanks a lot for this summary. A question about the requirement: do we or
> do we not have plan to support assigned device to the protected VM?
Good question, I assume that is stuff for the far far future.
>
> If yes. The fd based solution may need change the VFIO interface as well(
> though the fake swap entry solution need mess with VFIO too). Because:
>
> 1> KVM uses VFIO when assigning devices into a VM.
>
> 2> Not knowing which GPA ranges may be used by the VM as DMA buffer, all
> guest pages will have to be mapped in host IOMMU page table to host pages,
> which are pinned during the whole life cycle fo the VM.
>
> 3> IOMMU mapping is done during VM creation time by VFIO and IOMMU driver,
> in vfio_dma_do_map().
>
> 4> However, vfio_dma_do_map() needs the HVA to perform a GUP to get the HPA
> and pin the page.
>
> But if we are using fd based solution, not every GPA can have a HVA, thus
> the current VFIO interface to map and pin the GPA(IOVA) wont work. And I
> doubt if VFIO can be modified to support this easily.
I fully agree. Maybe Intel folks have some idea how that's supposed to
look like in the future.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-08-31 19:08 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 [this message]
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
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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