x86/hyperv: Initialize shared memory boundary in the Isolation VM.

Hyper-V exposes shared memory boundary via cpuid
HYPERV_CPUID_ISOLATION_CONFIG and store it in the
shared_gpa_boundary of ms_hyperv struct. This prepares
to share memory with host for SNP guest.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Link: https://lore.kernel.org/r/20211025122116.264793-3-ltykernel@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

include/asm-generic/mshyperv.h

@@ -35,7 +35,17 @@ struct ms_hyperv_info {
 	u32 max_vp_index;
 	u32 max_lp_index;
 	u32 isolation_config_a;
-	u32 isolation_config_b;
+	union {
+		u32 isolation_config_b;
+		struct {
+			u32 cvm_type : 4;
+			u32 reserved1 : 1;
+			u32 shared_gpa_boundary_active : 1;
+			u32 shared_gpa_boundary_bits : 6;
+			u32 reserved2 : 20;
+		};
+	};
+	u64 shared_gpa_boundary;
 };
 extern struct ms_hyperv_info ms_hyperv;