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<p class="MsoNormal"><b>From:</b> Jon Olson [mailto:jonolson@google.com] <br>
<b>Sent:</b> Friday, February 23, 2018 6:58 PM<br>
<b>To:</b> Larrew, Jesse <Jesse.Larrew@amd.com><br>
<b>Cc:</b> Castelino, Manohar R <manohar.r.castelino@intel.com>; Samuel Ortiz <sameo@linux.intel.com>; Hollingsworth, Brent <brent.hollingsworth@amd.com>; kata-dev@lists.katacontainers.io; Singh, Brijesh <brijesh.singh@amd.com>; Kaplan, David <David.Kaplan@amd.com>;
Woller, Thomas <thomas.woller@amd.com><br>
<b>Subject:</b> Re: [kata-dev] Kata with AMD Secure Encrypted Virtualization (SEV)<o:p></o:p></p>
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<p class="MsoNormal">On Fri, Feb 23, 2018 at 4:42 PM Larrew, Jesse <<a href="mailto:Jesse.Larrew@amd.com">Jesse.Larrew@amd.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">> From: Castelino, Manohar R [mailto:<a href="mailto:manohar.r.castelino@intel.com" target="_blank">manohar.r.castelino@intel.com</a>]<br>
> Sent: Friday, February 23, 2018 3:53 PM<br>
> To: Larrew, Jesse <<a href="mailto:Jesse.Larrew@amd.com" target="_blank">Jesse.Larrew@amd.com</a>>; Samuel Ortiz<br>
> <<a href="mailto:sameo@linux.intel.com" target="_blank">sameo@linux.intel.com</a>><br>
> Cc: Hollingsworth, Brent <<a href="mailto:brent.hollingsworth@amd.com" target="_blank">brent.hollingsworth@amd.com</a>>; Woller, Thomas<br>
> <<a href="mailto:thomas.woller@amd.com" target="_blank">thomas.woller@amd.com</a>>; Kaplan, David <<a href="mailto:David.Kaplan@amd.com" target="_blank">David.Kaplan@amd.com</a>>; kata-<br>
> <a href="mailto:dev@lists.katacontainers.io" target="_blank">dev@lists.katacontainers.io</a><br>
> Subject: RE: [kata-dev] Kata with AMD Secure Encrypted Virtualization (SEV)<br>
><br>
> Jesse,<br>
><br>
> > On EPYC, our IOMMU doesn't yet support SEV, so DMA to/from devices<br>
> needs<br>
> > to be done using unencrypted pages. It was easy to implement this using<br>
> the<br>
> > bounce buffers provided by SWIOTLB. As you guessed, a quick change to<br>
> > vring_use_dma_api() got virtio support working properly:<br>
><br>
> Clear Containers today supports direct device assignment via SRIOV.<br>
> This requires pre-allocation and pinning of VM memory.<br>
> Will this continue to work?<br>
><br>
> Also we have been working on reverse ballooning. i.e. free unused memory<br>
> from the VM back to the host. Is there is a way to get this to work with<br>
> encrypted memory<br>
><br>
> For more details about the patches<br>
> <a href="https://gist.github.com/sboeuf/fc71f0218a81997251ee0d7668df2bd9" target="_blank">
https://gist.github.com/sboeuf/fc71f0218a81997251ee0d7668df2bd9</a><br>
><br>
> -manohar<br>
><br>
><br>
<br>
Hi Manohar,<br>
<br>
SEV also requires the guest memory to be pre-allocated and pinned [1], so that's not a problem. As long as the PF drivers in the guest are using the dma apis, everything should continue to work.<o:p></o:p></p>
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<p class="MsoNormal">That's surprising -- I can see where reclaim would be challenging without something like a balloon, but why must the be initially backed? What happens if you leave a page unbacked and attempt to lazily back it on an EPT fault?<o:p></o:p></p>
<p class="MsoNormal"><b><i><o:p> </o:p></i></b></p>
<p class="MsoNormal"><b><i>[JDL] You’re right Jon. I misspoke above. The memory only needs to be pinned; the backing pages can be faulted in on demand. Sorry for the confusion.</i></b><o:p></o:p></p>
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<p class="MsoNormal"><br>
Similarly, the reverse ballooning patches should also work with SEV. In fact, I would argue that SEV compliments this feature by ensuring that physical page contents aren't exposed to the host when the guest uses MADV_FREE. I've CC'ed our KVM expert, Brijesh
Singh, just in case he sees something that I missed.<br>
<br>
Sincerely,<br>
Jesse<br>
<br>
[1] In order to ensure that memory blocks with identical data will encrypt to different ciphertext, SEV mixes the physical address into the encryption algorithm. As a result, if a page of memory is moved to a different physical address, it will not decrypt
properly. This also defeats block-move attacks on the guest memory, but it also requires all guest memory to be pinned.<br>
<br>
<o:p></o:p></p>
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