x86/dom0: improve PVH initrd and metadata placement

Don't assume there's going to be enough space at the tail of the
loaded kernel and instead try to find a suitable memory area where the
initrd and metadata can be loaded.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/dom0_build.c

@@ -490,6 +490,45 @@ static int __init pvh_populate_p2m(struct domain *d)
 #undef MB1_PAGES
 }
 
+static paddr_t find_memory(const struct domain *d, const struct elf_binary *elf,
+                           size_t size)
+{
+    paddr_t kernel_start = (paddr_t)elf->dest_base & PAGE_MASK;
+    paddr_t kernel_end = ROUNDUP((paddr_t)elf->dest_base + elf->dest_size,
+                                 PAGE_SIZE);
+    unsigned int i;
+
+    /*
+     * The memory map is sorted and all RAM regions starts and sizes are
+     * aligned to page boundaries.
+     */
+    for ( i = 0; i < d->arch.nr_e820; i++ )
+    {
+        paddr_t start, end = d->arch.e820[i].addr + d->arch.e820[i].size;
+
+        /* Don't use memory below 1MB, as it could overwrite BDA/EBDA/IBFT. */
+        if ( end <= MB(1) || d->arch.e820[i].type != E820_RAM )
+            continue;
+
+        start = MAX(ROUNDUP(d->arch.e820[i].addr, PAGE_SIZE), MB(1));
+
+        ASSERT(IS_ALIGNED(start, PAGE_SIZE) && IS_ALIGNED(end, PAGE_SIZE));
+
+        if ( end <= kernel_start || start >= kernel_end )
+            ; /* No overlap, nothing to do. */
+        /* Deal with the kernel already being loaded in the region. */
+        else if ( kernel_start - start > end - kernel_end )
+            end = kernel_start;
+        else
+            start = kernel_end;
+
+        if ( end - start >= size )
+            return start;
+    }
+
+    return INVALID_PADDR;
+}
+
 static int __init pvh_load_kernel(struct domain *d, const module_t *image,
                                   unsigned long image_headroom,
                                   module_t *initrd, void *image_base,
@@ -546,7 +585,24 @@ static int __init pvh_load_kernel(struct domain *d, const module_t *image,
         return rc;
     }
 
-    last_addr = ROUNDUP(parms.virt_kend - parms.virt_base, PAGE_SIZE);
+    /*
+     * Find a RAM region big enough (and that doesn't overlap with the loaded
+     * kernel) in order to load the initrd and the metadata. Note it could be
+     * split into smaller allocations, done as a single region in order to
+     * simplify it.
+     */
+    last_addr = find_memory(d, &elf, sizeof(start_info) +
+                            (initrd ? ROUNDUP(initrd->mod_end, PAGE_SIZE) +
+                                      sizeof(mod)
+                                    : 0) +
+                            (cmdline ? ROUNDUP(strlen(cmdline) + 1,
+                                               elf_64bit(&elf) ? 8 : 4)
+                                     : 0));
+    if ( last_addr == INVALID_PADDR )
+    {
+        printk("Unable to find a memory region to load initrd and metadata\n");
+        return -ENOMEM;
+    }
 
     if ( initrd != NULL )
     {