hypervisor: mhsv: Define software emulated TLB

A software emulated TLB. This is mostly used by
the instruction emulator to cache gva to gpa
translations passed from the hypervisor.

Co-Developed-by: Nuno Das Neves <nudasnev@microsoft.com>
Signed-off-by: Nuno Das Neves <nudasnev@microsoft.com>
Co-Developed-by: Praveen Paladugu <prapal@microsoft.com>
Signed-off-by: Praveen Paladugu <prapal@microsoft.com>
Co-Developed-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Co-Developed-by: Wei Liu <liuwe@microsoft.com>
Signed-off-by: Wei Liu <liuwe@microsoft.com>
Signed-off-by: Muminul Islam <muislam@microsoft.com>

hypervisor/src/mshv/mod.rs

@@ -327,6 +327,46 @@ impl hypervisor::Hypervisor for MshvHypervisor {
     }
 }
 
+#[derive(Clone)]
+// A software emulated TLB.
+// This is mostly used by the instruction emulator to cache gva to gpa translations
+// passed from the hypervisor.
+struct SoftTLB {
+    addr_map: HashMap<u64, u64>,
+}
+
+impl SoftTLB {
+    fn new() -> SoftTLB {
+        SoftTLB {
+            addr_map: HashMap::new(),
+        }
+    }
+
+    // Adds a gva -> gpa mapping into the TLB.
+    fn add_mapping(&mut self, gva: u64, gpa: u64) -> Result<(), PlatformError> {
+        *self.addr_map.entry(gva).or_insert(gpa) = gpa;
+        Ok(())
+    }
+
+    // Do the actual gva -> gpa translation
+    fn translate(&self, gva: u64) -> Result<u64, PlatformError> {
+        self.addr_map
+            .get(&gva)
+            .ok_or_else(|| PlatformError::UnmappedGVA(anyhow!("{:#?}", gva)))
+            .map(|v| *v)
+
+        // TODO Check if we could fallback to e.g. an hypercall for doing
+        // the translation for us.
+    }
+
+    // FLush the TLB, all mappings are removed.
+    fn flush(&mut self) -> Result<(), PlatformError> {
+        self.addr_map.clear();
+
+        Ok(())
+    }
+}
+
 #[allow(clippy::type_complexity)]
 /// Vcpu struct for Microsoft Hypervisor
 pub struct MshvVcpu {