x86/cpufeatures: Add "Allowed SEV Features" Feature

Add CPU feature detection for "Allowed SEV Features" to allow the
Hypervisor to enforce that SEV-ES and SEV-SNP guest VMs cannot
enable features (via SEV_FEATURES) that the Hypervisor does not
support or wish to be enabled.

Signed-off-by: Kishon Vijay Abraham I <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Reviewed-by: Pankaj Gupta <[email protected]>
Acked-by: Borislav Petkov (AMD) <[email protected]>
Signed-off-by: Kim Phillips <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: kishonvijayabraham

arch/x86/include/asm/cpufeatures.h

@@ -446,6 +446,7 @@
 #define X86_FEATURE_DEBUG_SWAP		(19*32+14) /* "debug_swap" SEV-ES full debug state swap support */
 #define X86_FEATURE_RMPREAD		(19*32+21) /* RMPREAD instruction */
 #define X86_FEATURE_SEGMENTED_RMP	(19*32+23) /* Segmented RMP support */
+#define X86_FEATURE_ALLOWED_SEV_FEATURES (19*32+27) /* Allowed SEV Features */
 #define X86_FEATURE_SVSM		(19*32+28) /* "svsm" SVSM present */
 #define X86_FEATURE_HV_INUSE_WR_ALLOWED	(19*32+30) /* Allow Write to in-use hypervisor-owned pages */