feat(vmm): add offset/gpa conversion functions

This is because vCPUs reason in GPAs while the secret-free UFFD
protocol is guest_memfd-offset-based.

Note that offset_to_gpa is not used yet, but will likely be needed to
support async PF to pass the GPA to a new ioctl when notifying KVM of a
fault resolution.

Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>

Author: kalyazin

src/vmm/src/vstate/memory.rs

@@ -787,6 +787,12 @@ where
 
     /// Discards a memory range, freeing up memory pages
     fn discard_range(&self, addr: GuestAddress, range_len: usize) -> Result<(), GuestMemoryError>;
+
+    /// Convert guest physical address to file offset
+    fn gpa_to_offset(&self, gpa: GuestAddress) -> Option<u64>;
+
+    /// Convert file offset to guest physical address
+    fn offset_to_gpa(&self, offset: u64) -> Option<GuestAddress>;
 }
 
 /// State of a guest memory region saved to file/buffer.
@@ -964,6 +970,33 @@ impl GuestMemoryExtension for GuestMemoryMmap {
             region.discard_range(start, len)
         })
     }
+
+    /// Convert guest physical address to file offset
+    fn gpa_to_offset(&self, gpa: GuestAddress) -> Option<u64> {
+        self.find_region(gpa).map(|r| {
+            gpa.0 - r.start_addr().0 + r.file_offset().expect("File offset is None").start()
+        })
+    }
+
+    /// Convert file offset to guest physical address
+    fn offset_to_gpa(&self, offset: u64) -> Option<GuestAddress> {
+        self.iter().find_map(|region| {
+            if let Some(reg_offset) = region.file_offset() {
+                let region_start = reg_offset.start();
+                let region_size = region.size();
+
+                if offset >= region_start && offset < region_start + region_size as u64 {
+                    Some(GuestAddress(
+                        region.start_addr().0 + (offset - region_start),
+                    ))
+                } else {
+                    None
+                }
+            } else {
+                None
+            }
+        })
+    }
 }
 
 /// Creates a memfd of the given size and huge pages configuration