Re: [PATCH v8 00/18] Add AMD SEV guest live migration support

Steve Rutherford
2020-06-01T20:03:03Z

On Mon, May 18, 2020 at 12:07 PM Ashish Kalra <ashish.kalra@amd.com> wrote:
>
> Hello All,
>
> Any other feedback, review or comments on this patch-set ?
>
> Thanks,
> Ashish
>
> On Tue, May 05, 2020 at 09:13:49PM +0000, Ashish Kalra wrote:
> > From: Ashish Kalra <ashish.kalra@amd.com>
> >
> > 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 new ioctls KVM_{SET,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.
> >
> > This section descibes how the SEV live migration feature is negotiated
> > between the host and guest, the host indicates this feature support via
> > KVM_FEATURE_CPUID. The guest firmware (OVMF) detects this feature and
> > sets a UEFI enviroment variable indicating OVMF support for live
> > migration, the guest kernel also detects the host support for this
> > feature via cpuid and in case of an EFI boot verifies if OVMF also
> > supports this feature by getting the UEFI enviroment variable and if it
> > set then enables live migration feature on host by writing to a custom
> > MSR, if not booted under EFI, then it simply enables the feature by
> > again writing to the custom MSR. The host returns error as part of
> > SET_PAGE_ENC_BITMAP ioctl if guest has not enabled live migration.
> >
> > A branch containing these patches is available here:
> > https://github.com/AMDESE/linux/tree/sev-migration-v8
> >
> > [1] https://developer.amd.com/wp-content/resources/55766.PDF
> >
> > Changes since v7:
> > - Removed the hypervisor specific hypercall/paravirt callback for
> > SEV live migration and moved back to calling kvm_sev_hypercall3
> > directly.
> > - Fix build errors as
> > Reported-by: kbuild test robot <lkp@intel.com>, specifically fixed
> > build error when CONFIG_HYPERVISOR_GUEST=y and
> > CONFIG_AMD_MEM_ENCRYPT=n.
> > - Implicitly enabled live migration for incoming VM(s) to handle
> > A->B->C->... VM migrations.
> > - Fixed Documentation as per comments on v6 patches.
> > - Fixed error return path in sev_send_update_data() as per comments
> > on v6 patches.
> >
> > Changes since v6:
> > - Rebasing to mainline and refactoring to the new split SVM
> > infrastructre.
> > - Move to static allocation of the unified Page Encryption bitmap
> > instead of the dynamic resizing of the bitmap, the static allocation
> > is done implicitly by extending kvm_arch_commit_memory_region() callack
> > to add svm specific x86_ops which can read the userspace provided memory
> > region/memslots and calculate the amount of guest RAM managed by the KVM
> > and grow the bitmap.
> > - Fixed KVM_SET_PAGE_ENC_BITMAP ioctl to set the whole bitmap instead
> > of simply clearing specific bits.
> > - Removed KVM_PAGE_ENC_BITMAP_RESET ioctl, which is now performed using
> > KVM_SET_PAGE_ENC_BITMAP.
> > - Extended guest support for enabling Live Migration feature by adding a
> > check for UEFI environment variable indicating OVMF support for Live
> > Migration feature and additionally checking for KVM capability for the
> > same feature. If not booted under EFI, then we simply check for KVM
> > capability.
> > - Add hypervisor specific hypercall for SEV live migration by adding
> > a new paravirt callback as part of x86_hyper_runtime.
> > (x86 hypervisor specific runtime callbacks)
> > - Moving MSR handling for MSR_KVM_SEV_LIVE_MIG_EN into svm/sev code
> > and adding check for SEV live migration enabled by guest in the
> > KVM_GET_PAGE_ENC_BITMAP ioctl.
> > - Instead of the complete __bss_decrypted section, only specific variables
> > such as hv_clock_boot and wall_clock are marked as decrypted in the
> > page encryption bitmap
> >
> > Changes since v5:
> > - Fix build errors as
> > Reported-by: kbuild test robot <lkp@intel.com>
> >
> > Changes since v4:
> > - Host support has been added to extend KVM capabilities/feature bits to
> > include a new KVM_FEATURE_SEV_LIVE_MIGRATION, which the guest can
> > query for host-side support for SEV live migration and a new custom MSR
> > MSR_KVM_SEV_LIVE_MIG_EN is added for guest to enable the SEV live
> > migration feature.
> > - Ensure that _bss_decrypted section is marked as decrypted in the
> > page encryption bitmap.
> > - Fixing KVM_GET_PAGE_ENC_BITMAP ioctl to return the correct bitmap
> > as per the number of pages being requested by the user. Ensure that
> > we only copy bmap->num_pages bytes in the userspace buffer, if
> > bmap->num_pages is not byte aligned we read the trailing bits
> > from the userspace and copy those bits as is. This fixes guest
> > page(s) corruption issues observed after migration completion.
> > - Add kexec support for SEV Live Migration to reset the host's
> > page encryption bitmap related to kernel specific page encryption
> > status settings before we load a new kernel by kexec. We cannot
> > reset the complete page encryption bitmap here as we need to
> > retain the UEFI/OVMF firmware specific settings.
> >
> > Changes since v3:
> > - Rebasing to mainline and testing.
> > - Adding a new KVM_PAGE_ENC_BITMAP_RESET ioctl, which resets the
> > page encryption bitmap on a guest reboot event.
> > - Adding a more reliable sanity check for GPA range being passed to
> > the hypercall to ensure that guest MMIO ranges are also marked
> > in the page encryption bitmap.
> >
> > Changes since v2:
> > - reset the page encryption bitmap on vcpu reboot
> >
> > Changes since v1:
> > - Add support to share the page encryption between the source and target
> > machine.
> > - Fix review feedbacks from Tom Lendacky.
> > - Add check to limit the session blob length.
> > - Update KVM_GET_PAGE_ENC_BITMAP icotl to use the base_gfn instead of
> > the memory slot when querying the bitmap.
> >
> > Ashish Kalra (7):
> > KVM: SVM: Add support for static allocation of unified Page Encryption
> > Bitmap.
> > KVM: x86: Introduce new KVM_FEATURE_SEV_LIVE_MIGRATION feature &
> > Custom MSR.
> > EFI: Introduce the new AMD Memory Encryption GUID.
> > KVM: x86: Add guest support for detecting and enabling SEV Live
> > Migration feature.
> > KVM: x86: Mark _bss_decrypted section variables as decrypted in page
> > encryption bitmap.
> > KVM: x86: Add kexec support for SEV Live Migration.
> > KVM: SVM: Enable SEV live migration feature implicitly on Incoming
> > VM(s).
> >
> > Brijesh Singh (11):
> > 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
> > KVM: x86: Introduce KVM_SET_PAGE_ENC_BITMAP ioctl
> >
> > .../virt/kvm/amd-memory-encryption.rst | 120 +++
> > Documentation/virt/kvm/api.rst | 71 ++
> > Documentation/virt/kvm/cpuid.rst | 5 +
> > Documentation/virt/kvm/hypercalls.rst | 15 +
> > Documentation/virt/kvm/msr.rst | 10 +
> > arch/x86/include/asm/kvm_host.h | 7 +
> > arch/x86/include/asm/kvm_para.h | 12 +
> > arch/x86/include/asm/mem_encrypt.h | 11 +
> > arch/x86/include/asm/paravirt.h | 10 +
> > arch/x86/include/asm/paravirt_types.h | 2 +
> > arch/x86/include/uapi/asm/kvm_para.h | 5 +
> > arch/x86/kernel/kvm.c | 90 +++
> > arch/x86/kernel/kvmclock.c | 12 +
> > arch/x86/kernel/paravirt.c | 1 +
> > arch/x86/kvm/svm/sev.c | 732 +++++++++++++++++-
> > arch/x86/kvm/svm/svm.c | 21 +
> > arch/x86/kvm/svm/svm.h | 9 +
> > arch/x86/kvm/vmx/vmx.c | 1 +
> > arch/x86/kvm/x86.c | 35 +
> > arch/x86/mm/mem_encrypt.c | 68 +-
> > arch/x86/mm/pat/set_memory.c | 7 +
> > include/linux/efi.h | 1 +
> > include/linux/psp-sev.h | 8 +-
> > include/uapi/linux/kvm.h | 52 ++
> > include/uapi/linux/kvm_para.h | 1 +
> > 25 files changed, 1297 insertions(+), 9 deletions(-)
> >
> > --
> > 2.17.1
> >

Hey all,
These patches look pretty reasonable at this point. What's the next
step for getting them merged?

Thanks,
Steve