not enable SME, then Linux will not be able to activate memory encryption, even
if configured to do so by default or the mem_encrypt=on command line parameter
is specified.
+
+Secure Nested Paging (SNP)
+==========================
+
+SEV-SNP introduces new features (SEV_FEATURES[1:63]) which can be enabled
+by the hypervisor for security enhancements. Some of these features need
+guest side implementation to function correctly. The below table lists the
+expected guest behavior with various possible scenarios of guest/hypervisor
+SNP feature support.
+
++-----------------+---------------+---------------+------------------+
+| Feature Enabled | Guest needs | Guest has | Guest boot |
+| by the HV | implementation| implementation| behaviour |
++=================+===============+===============+==================+
+| No | No | No | Boot |
+| | | | |
++-----------------+---------------+---------------+------------------+
+| No | Yes | No | Boot |
+| | | | |
++-----------------+---------------+---------------+------------------+
+| No | Yes | Yes | Boot |
+| | | | |
++-----------------+---------------+---------------+------------------+
+| Yes | No | No | Boot with |
+| | | | feature enabled |
++-----------------+---------------+---------------+------------------+
+| Yes | Yes | No | Graceful boot |
+| | | | failure |
++-----------------+---------------+---------------+------------------+
+| Yes | Yes | Yes | Boot with |
+| | | | feature enabled |
++-----------------+---------------+---------------+------------------+
+
+More details in AMD64 APM[1] Vol 2: 15.34.10 SEV_STATUS MSR
+
+[1] https://www.amd.com/system/files/TechDocs/40332.pdf