AMD has submitted a similar patch to the Linux kernel, now there is support for AMD SEV in UEFI.
[RFC PATCH v1 0/5] x86: Secure Encrypted Virtualization (AMD)
This RFC series provides support for AMD’s new Secure Encrypted Virtualization (SEV) feature. SEV is an extension to the AMD-V architecture which supports running multiple VMs under the control of a hypervisor. The SEV feature allows the memory contents of a virtual machine (VM) to be transparently encrypted with a key unique to the guest VM. The memory controller contains a high performance encryption engine which can be programmed with multiple keys for use by a different VMs in the system. The programming and management of these keys is handled by the AMD Secure Processor firmware which exposes a commands for these tasks. 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. Certain types of memory (namely instruction pages and guest page tables) are always treated as private memory by the hardware. For data memory, SEV guest VMs can choose which pages they would like to be private. The choice is done using the standard CPU page tables using the C-bit, and is fully controlled by the guest. Due to security reasons all the DMA operations inside the guest must be performed on shared pages (C-bit clear). Note that since C-bit is only controllable by the guest OS when it is operating in 64-bit or 32-bit PAE mode, in all other modes the SEV hardware forces the C-bit to a 1. KVM SEV RFC  extends the KVM_FEATURE cpuid instruction to indicate whether SEV is enabled. When SEV is enabled then OVMF can use cpuid Fn8000_001F[BX] to get the C-bit position in PTE.
AMD Memory Encryption whitepaper:
AMD64 Architecture Programmer’s Manual (SME is section 7.10, SEV is section 15.34):
Secure Encrypted Virutualization Key Management: