pvh: Do not attempt PVH boot if kernel_offset is requested

In x86, the kernel_offset parameter is used to request that the
kernel is loaded in guest memory at a fixed offset from the default
load address encoded in the phdr.p_paddr field of the Elf header.

Do not attempt to look for a PVH entry point if a load offset has
been requested using kernel_offset, since PVH expects the kernel to
be loaded at the default load address.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>

Author: aljimenezb

src/loader/x86_64/elf/mod.rs

@@ -130,7 +130,8 @@ impl Elf {
 impl KernelLoader for Elf {
     /// Loads a kernel from a vmlinux elf image into guest memory.
     ///
-    /// The kernel is loaded into guest memory at offset `phdr.p_paddr` specified by the elf image.
+    /// By default, the kernel is loaded into guest memory at offset `phdr.p_paddr` specified by the elf image.
+    /// When used, `kernel_offset` specifies a fixed offset from `phdr.p_paddr` at which to load the kernel.
     ///
     /// # Arguments
     ///
@@ -212,7 +213,12 @@ impl KernelLoader for Elf {
         // Read in each section pointed to by the program headers.
         for phdr in phdrs {
             if phdr.p_type != elf::PT_LOAD || phdr.p_filesz == 0 {
-                if phdr.p_type == elf::PT_NOTE {
+                // The PVH boot protocol currently requires that the kernel is loaded at
+                // the default kernel load address in guest memory (specified at kernel
+                // build by the value of CONFIG_PHYSICAL_START). Therefore, only attempt
+                // to use PVH if an offset from the default load address has not been
+                // requested using the kernel_offset parameter.
+                if phdr.p_type == elf::PT_NOTE && kernel_offset.is_none() {
                     // This segment describes a Note, check if PVH entry point is encoded.
                     loader_result.pvh_entry_addr = parse_elf_note(&phdr, kernel_image)?;
                 }