Performance measurement w/ and w/o host-side memory encryption

[mmisono]

When performing I/O, the bounce buffer can be encrypted with the host key. That might introduce some additional overhead. Measure performance w/ and w/o host-side memory encryption.

Detail

We can have following configurations.

	memory type	AMD SEV-SNP	Intel TDX
Guest-side encryption	private	Guest C-bit: 1 (Host C-bit: don't care)	Guest shared-bit: 0 (Host configuration: don't care)
Host-side encryption	shared	Guest C-bit: 0, Host C-bit:1	Guest shared-bit: 1, Host TME Bypass off
No encryption.	shared	Guest C-bit: 0, Host C-bit: 0	Guest shared-bit: 1, Host TME Bypass on

• Technically TDX host can encrypt its memory with shared keyIDs, which BIOS configures. TMEBypass disables memory encryption for the keyID 0.
• AMD disables host side memory encryption by default
  • kernel config: CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT
  • kernel parameters: mem_encrypt=[on,off]

TODO

• Check the default configuration of the host side in AMD SEV-SNP
• Measure performance

[enterJazz]

Here are current tdx tme bypass measurements:
tdx.log
tdx-tme-bypass.log