x86/sev: Check SEV-SNP features support
Version 2 of the GHCB specification added the advertisement of features that are supported by the hypervisor. If the hypervisor supports SEV-SNP then it must set the SEV-SNP features bit to indicate that the base functionality is supported. Check that feature bit while establishing the GHCB; if failed, terminate the guest. Version 2 of the GHCB specification adds several new Non-Automatic Exits (NAEs), most of them are optional except the hypervisor feature. Now that the hypervisor feature NAE is implemented, bump the GHCB maximum supported protocol version. While at it, move the GHCB protocol negotiation check from the #VC exception handler to sev_enable() so that all feature detection happens before the first #VC exception. While at it, document why the GHCB page cannot be setup from load_stage2_idt(). [ bp: Massage commit message. ] Signed-off-by:Brijesh Singh <brijesh.singh@amd.com> Signed-off-by:
Borislav Petkov <bp@suse.de> Link: https://lore.kernel.org/r/20220307213356.2797205-13-brijesh.singh@amd.com
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