Re: [RFC PATCH v1 00/10] Add AMD SEV guest live migration support

[Steve Rutherford <srutherford@google.com>]

On Wed, Apr 24, 2019 at 9:10 AM Singh, Brijesh <brijesh.singh@amd.com> wrote:
>
> The series add support for AMD SEV guest live migration commands. To protect the
> confidentiality of an SEV protected guest memory while in transit we need to
> use the SEV commands defined in SEV API spec [1].
>
> SEV guest VMs have the concept of private and shared memory. Private memory
> is encrypted with the guest-specific key, while shared memory may be encrypted
> with hypervisor key. The commands provided by the SEV FW are meant to be used
> for the private memory only. The patch series introduces a new hypercall.
> The guest OS can use this hypercall to notify the page encryption status.
> If the page is encrypted with guest specific-key then we use SEV command during
> the migration. If page is not encrypted then fallback to default.
>
> The patch adds a new ioctl KVM_GET_PAGE_ENC_BITMAP. The ioctl can be used
> by the qemu to get the page encrypted bitmap. Qemu can consult this bitmap
> during the migration to know whether the page is encrypted.
>
> [1] https://developer.amd.com/wp-content/resources/55766.PDF
>
> The series is tested with the Qemu, I am in process of cleaning
> up the Qemu code and will submit soon.
>
> While implementing the migration I stumbled on the follow question:
>
> - Since there is a guest OS changes required to support the migration,
>   so how do we know whether guest OS is updated? Should we extend KVM
>   capabilities/feature bits to check this?
>
> TODO:
>  - add an ioctl to build encryption bitmap. The encryption bitmap is built during
>    the guest bootup/execution. We should provide an ioctl so that destination
>    can build the bitmap as it receives the pages.
>  - reset the bitmap on guest reboot.
>
> The complete tree with patch is available at:
> https://github.com/codomania/kvm/tree/sev-migration-rfc-v1
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
>
> Brijesh Singh (10):
>   KVM: SVM: Add KVM_SEV SEND_START command
>   KVM: SVM: Add KVM_SEND_UPDATE_DATA command
>   KVM: SVM: Add KVM_SEV_SEND_FINISH command
>   KVM: SVM: Add support for KVM_SEV_RECEIVE_START command
>   KVM: SVM: Add KVM_SEV_RECEIVE_UPDATE_DATA command
>   KVM: SVM: Add KVM_SEV_RECEIVE_FINISH command
>   KVM: x86: Add AMD SEV specific Hypercall3
>   KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall
>   KVM: x86: Introduce KVM_GET_PAGE_ENC_BITMAP ioctl
>   mm: x86: Invoke hypercall when page encryption status is changed
>
>  .../virtual/kvm/amd-memory-encryption.rst     | 116 ++++
>  Documentation/virtual/kvm/hypercalls.txt      |  14 +
>  arch/x86/include/asm/kvm_host.h               |   3 +
>  arch/x86/include/asm/kvm_para.h               |  12 +
>  arch/x86/include/asm/mem_encrypt.h            |   3 +
>  arch/x86/kvm/svm.c                            | 560 +++++++++++++++++-
>  arch/x86/kvm/vmx/vmx.c                        |   1 +
>  arch/x86/kvm/x86.c                            |  17 +
>  arch/x86/mm/mem_encrypt.c                     |  45 +-
>  arch/x86/mm/pageattr.c                        |  15 +
>  include/uapi/linux/kvm.h                      |  51 ++
>  include/uapi/linux/kvm_para.h                 |   1 +
>  12 files changed, 834 insertions(+), 4 deletions(-)
>
> --
> 2.17.1
>

What's the back-of-the-envelope marginal cost of transferring a 16kB
region from one host to another? I'm interested in what the end to end
migration perf changes look like for this. If you have measured
migration perf, I'm interested in that also.