Intra host migration provides a low-cost mechanism for userspace VMM upgrades. It is an alternative to traditional (i.e., remote) live migration. Whereas remote migration handles moving a guest to a new host, intra host migration only handles moving a guest to a new userspace VMM within a host. This can be used to update, rollback, change flags of the VMM, etc. The lower cost compared to live migration comes from the fact that the guest's memory does not need to be copied between processes. A handle to the guest memory simply gets passed to the new VMM, this could be done via /dev/shm with share=on or similar feature. The guest state can be transferred from an old VMM to a new VMM as follows: 1. Export guest state from KVM to the old user-space VMM via a getter user-space/kernel API 2. Transfer guest state from old VMM to new VMM via IPC communication 3. Import guest state into KVM from the new user-space VMM via a setter user-space/kernel API VMMs by exporting from KVM using getters, sending that data to the new VMM, then setting it again in KVM. In the common case for intra host migration, we can rely on the normal ioctls for passing data from one VMM to the next. SEV, SEV-ES, and other confidential compute environments make most of this information opaque, and render KVM ioctls such as "KVM_GET_REGS" irrelevant. As a result, we need the ability to pass this opaque metadata from one VMM to the next. The easiest way to do this is to leave this data in the kernel, and transfer ownership of the metadata from one KVM VM (or vCPU) to the next. For example, we need to move the SEV enabled ASID, VMSAs, and GHCB metadata from one VMM to the next. In general, we need to be able to hand off any data that would be unsafe/impossible for the kernel to hand directly to userspace (and cannot be reproduced using data that can be handed safely to userspace). For the intra host operation the SEV required metadata, the source VM FD is sent to the target VMM. The target VMM calls the new cap ioctl with the source VM FD, KVM then moves all the SEV state to the target VM from the source VM. V5: * Fix up locking scheme * Address marcorr@ comments. V4: * Move to seanjc@'s suggestion of source VM FD based single ioctl design. v3: * Fix memory leak found by dan.carpenter@ v2: * Added marcorr@ reviewed by tag * Renamed function introduced in 1/3 * Edited with seanjc@'s review comments ** Cleaned up WARN usage ** Userspace makes random token now * Edited with brijesh.singh@'s review comments ** Checks for different LAUNCH_* states in send function v1: https://lore.kernel.org/kvm/20210621163118.1040170-1-pgonda@xxxxxxxxxx/ Peter Gonda (2): KVM, SEV: Add support for SEV intra host migration KVM, SEV: Add support for SEV-ES intra host migration Documentation/virt/kvm/api.rst | 15 +++ arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/svm/sev.c | 157 ++++++++++++++++++++++++++++++++ arch/x86/kvm/svm/svm.c | 1 + arch/x86/kvm/svm/svm.h | 2 + arch/x86/kvm/x86.c | 5 + include/uapi/linux/kvm.h | 1 + 7 files changed, 182 insertions(+) base-commit: a3e0b8bd99ab Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Sean Christopherson <seanjc@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx> Cc: Brijesh Singh <brijesh.singh@xxxxxxx> Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx> Cc: Jim Mattson <jmattson@xxxxxxxxxx> Cc: Joerg Roedel <joro@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: kvm@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx -- 2.33.0.rc2.250.ged5fa647cd-goog
