docs: Add SEV-ES documentation to amd-memory-encryption.txt

Update the amd-memory-encryption.txt file with information about SEV-ES,
including how to launch an SEV-ES guest and some of the differences
between SEV and SEV-ES guests in regards to launching and measuring the
guest.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Connor Kuehl <ckuehl@redhat.com>
Message-Id: <fa1825a5eb0290eac4712cde75ba4c6829946eac.1619208498.git.thomas.lendacky@amd.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

docs/amd-memory-encryption.txt

@@ -15,6 +15,13 @@ includes commands for launching, snapshotting, migrating and debugging the
 encrypted guest. These SEV commands can be issued via KVM_MEMORY_ENCRYPT_OP
 ioctls.
 
+Secure Encrypted Virtualization - Encrypted State (SEV-ES) builds on the SEV
+support to additionally protect the guest register state. In order to allow a
+hypervisor to perform functions on behalf of a guest, there is architectural
+support for notifying a guest's operating system when certain types of VMEXITs
+are about to occur. This allows the guest to selectively share information with
+the hypervisor to satisfy the requested function.
+
 Launching
 ---------
 Boot images (such as bios) must be encrypted before a guest can be booted. The
@@ -24,6 +31,9 @@ together generate a fresh memory encryption key for the VM, encrypt the boot
 images and provide a measurement than can be used as an attestation of a
 successful launch.
 
+For a SEV-ES guest, the LAUNCH_UPDATE_VMSA command is also used to encrypt the
+guest register state, or VM save area (VMSA), for all of the guest vCPUs.
+
 LAUNCH_START is called first to create a cryptographic launch context within
 the firmware. To create this context, guest owner must provide a guest policy,
 its public Diffie-Hellman key (PDH) and session parameters. These inputs
@@ -40,6 +50,12 @@ The guest policy can be provided via the 'policy' property (see below)
 # ${QEMU} \
    sev-guest,id=sev0,policy=0x1...\
 
+Setting the "SEV-ES required" policy bit (bit 2) will launch the guest as a
+SEV-ES guest (see below)
+
+# ${QEMU} \
+   sev-guest,id=sev0,policy=0x5...\
+
 The guest owner provided DH certificate and session parameters will be used to
 establish a cryptographic session with the guest owner to negotiate keys used
 for the attestation.
@@ -55,13 +71,19 @@ created via the LAUNCH_START command. If required, this command can be called
 multiple times to encrypt different memory regions. The command also calculates
 the measurement of the memory contents as it encrypts.
 
-LAUNCH_MEASURE can be used to retrieve the measurement of encrypted memory.
+LAUNCH_UPDATE_VMSA encrypts all the vCPU VMSAs for a SEV-ES guest using the
-This measurement is a signature of the memory contents that can be sent to the
+cryptographic context created via the LAUNCH_START command. The command also
-guest owner as an attestation that the memory was encrypted correctly by the
+calculates the measurement of the VMSAs as it encrypts them.
-firmware. The guest owner may wait to provide the guest confidential information
+
-until it can verify the attestation measurement. Since the guest owner knows the
+LAUNCH_MEASURE can be used to retrieve the measurement of encrypted memory and,
-initial contents of the guest at boot, the attestation measurement can be
+for a SEV-ES guest, encrypted VMSAs. This measurement is a signature of the
-verified by comparing it to what the guest owner expects.
+memory contents and, for a SEV-ES guest, the VMSA contents, that can be sent
+to the guest owner as an attestation that the memory and VMSAs were encrypted
+correctly by the firmware. The guest owner may wait to provide the guest
+confidential information until it can verify the attestation measurement.
+Since the guest owner knows the initial contents of the guest at boot, the
+attestation measurement can be verified by comparing it to what the guest owner
+expects.
 
 LAUNCH_FINISH finalizes the guest launch and destroys the cryptographic
 context.
@@ -75,6 +97,22 @@ To launch a SEV guest
     -machine ...,confidential-guest-support=sev0 \
     -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1
 
+To launch a SEV-ES guest
+
+# ${QEMU} \
+    -machine ...,confidential-guest-support=sev0 \
+    -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1,policy=0x5
+
+An SEV-ES guest has some restrictions as compared to a SEV guest. Because the
+guest register state is encrypted and cannot be updated by the VMM/hypervisor,
+a SEV-ES guest:
+ - Does not support SMM - SMM support requires updating the guest register
+   state.
+ - Does not support reboot - a system reset requires updating the guest register
+   state.
+ - Requires in-kernel irqchip - the burden is placed on the hypervisor to
+   manage booting APs.
+
 Debugging
 -----------
 Since the memory contents of a SEV guest are encrypted, hypervisor access to
@@ -101,8 +139,10 @@ Secure Encrypted Virtualization Key Management:
 
 KVM Forum slides:
 http://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf
+https://www.linux-kvm.org/images/9/94/Extending-Secure-Encrypted-Virtualization-with-SEV-ES-Thomas-Lendacky-AMD.pdf
 
 AMD64 Architecture Programmer's Manual:
    http://support.amd.com/TechDocs/24593.pdf
    SME is section 7.10
    SEV is section 15.34
+   SEV-ES is section 15.35