[PATCH] x86/PVH: account for module command line length

[Jan Beulich <jbeulich@xxxxxxxx>]

As per observation in practice, initrd->cmdline_pa is not normally zero.
Hence so far we always appended at least one byte. That alone may
already render insufficient the "allocation" made by find_memory().
Things would be worse when there's actually a (perhaps long) command
line.

Skip setup when the command line is empty. Amend the "allocation" size
by padding and actual size of module command line.

Fixes: 0ecb8eb09f9f ("x86/pvh: pass module command line to dom0")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -712,7 +712,15 @@ static int __init pvh_load_kernel(
      * simplify it.
      */
     last_addr = find_memory(d, &elf, sizeof(start_info) +
-                            (initrd ? ROUNDUP(initrd_len, PAGE_SIZE) +
+                            (initrd ? ROUNDUP(ROUNDUP(initrd_len,
+                                                      elf_64bit(&elf) ? 8 : 4) 
+
+                                              (initrd->cmdline_pa &&
+                                               strlen(__va(initrd->
+                                                           cmdline_pa))
+                                               ? strlen(__va(initrd->
+                                                             cmdline_pa)) + 1
+                                               : 0),
+                                              PAGE_SIZE) +
                                       sizeof(mod)
                                     : 0) +
                             (cmdline ? ROUNDUP(strlen(cmdline) + 1,
@@ -740,16 +748,19 @@ static int __init pvh_load_kernel(
         if ( initrd->cmdline_pa )
         {
             char *str = __va(initrd->cmdline_pa);
-            size_t len = strlen(str) + 1;
+            size_t len = strlen(str);
 
-            rc = hvm_copy_to_guest_phys(last_addr, str, len, v);
-            if ( rc )
+            if ( len++ )
             {
-                printk("Unable to copy module command line\n");
-                return rc;
+                rc = hvm_copy_to_guest_phys(last_addr, str, len, v);
+                if ( rc )
+                {
+                    printk("Unable to copy module command line\n");
+                    return rc;
+                }
+                mod.cmdline_paddr = last_addr;
+                last_addr += len;
             }
-            mod.cmdline_paddr = last_addr;
-            last_addr += len;
         }
         last_addr = ROUNDUP(last_addr, PAGE_SIZE);
     }