Configure guest vTOM when configured by IGVM parameters

Signed-off-by: Jon Lange <jlange@microsoft.com>

igvm_params/src/lib.rs

@@ -88,6 +88,9 @@ pub struct IgvmParamBlock {
 
     /// The guest physical address of the base of the kernel memory region.
     pub kernel_base: u64,
+
+    /// The value of vTOM used by the guest, or zero if not used.
+    pub vtom: u64,
 }
 
 /// The IGVM context page is a measured page that is used to specify the start

src/igvm_params.rs

@@ -262,6 +262,12 @@ impl IgvmParams<'_> {
             vmsa.es = vmsa.ds;
             vmsa.fs = vmsa.ds;
             vmsa.gs = vmsa.ds;
+
+            // Configure vTOM if reqqested.
+            if self.igvm_param_block.vtom != 0 {
+                vmsa.vtom = self.igvm_param_block.vtom;
+                vmsa.sev_features |= 2; // VTOM feature
+            }
         }
     }
 }