[PATCH v3] 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. Along these lines
also skip initrd setup when the initrd is zero size.

Fixes: 0ecb8eb09f9f ("x86/pvh: pass module command line to dom0")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v3: Permit empty initrd with non-empty module command line again.
v2: Use elf_round_up(). Introduce initrd_cmdline local. Re-base.

--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -652,9 +652,10 @@ static int __init pvh_load_kernel(
     unsigned long image_len = image->size;
     unsigned long initrd_len = initrd ? initrd->size : 0;
     const char *cmdline = image->cmdline_pa ? __va(image->cmdline_pa) : NULL;
+    const char *initrd_cmdline = NULL;
     struct elf_binary elf;
     struct elf_dom_parms parms;
-    size_t extra_space;
+    size_t extra_space = 0;
     paddr_t last_addr;
     struct hvm_start_info start_info = { 0 };
     struct hvm_modlist_entry mod = { 0 };
@@ -712,10 +713,26 @@ static int __init pvh_load_kernel(
      * split into smaller allocations, done as a single region in order to
      * simplify it.
      */
-    extra_space = sizeof(start_info);
-
     if ( initrd )
-        extra_space += sizeof(mod) + ROUNDUP(initrd_len, PAGE_SIZE);
+    {
+        extra_space = elf_round_up(&elf, initrd_len);
+
+        if ( initrd->cmdline_pa )
+        {
+            initrd_cmdline = __va(initrd->cmdline_pa);
+            if ( !*initrd_cmdline )
+                initrd_cmdline = NULL;
+        }
+        if ( initrd_cmdline )
+            extra_space += strlen(initrd_cmdline) + 1;
+
+        if ( extra_space )
+            extra_space = ROUNDUP(extra_space, PAGE_SIZE) + sizeof(mod);
+        else
+            initrd = NULL;
+    }
+
+    extra_space += sizeof(start_info);
 
     if ( cmdline )
         extra_space += elf_round_up(&elf, strlen(cmdline) + 1);
@@ -740,12 +757,11 @@ static int __init pvh_load_kernel(
         mod.paddr = last_addr;
         mod.size = initrd_len;
         last_addr += elf_round_up(&elf, initrd_len);
-        if ( initrd->cmdline_pa )
+        if ( initrd_cmdline )
         {
-            char *str = __va(initrd->cmdline_pa);
-            size_t len = strlen(str) + 1;
+            size_t len = strlen(initrd_cmdline) + 1;
 
-            rc = hvm_copy_to_guest_phys(last_addr, str, len, v);
+            rc = hvm_copy_to_guest_phys(last_addr, initrd_cmdline, len, v);
             if ( rc )
             {
                 printk("Unable to copy module command line\n");