xen: eliminate scalability issues from initrd handling

Size restrictions native kernels wouldn't have resulted from the initrd
getting mapped into the initial mapping. The kernel doesn't really need
the initrd to be mapped, so use infrastructure available in Xen to avoid
the mapping and hence the restriction.
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

arch/x86/xen/enlighten.c

@@ -1519,6 +1519,7 @@ static void __init xen_pvh_early_guest_init(void)
 asmlinkage __visible void __init xen_start_kernel(void)
 {
 	struct physdev_set_iopl set_iopl;
+	unsigned long initrd_start = 0;
 	int rc;
 
 	if (!xen_start_info)
@@ -1665,10 +1666,16 @@ asmlinkage __visible void __init xen_start_kernel(void)
 	new_cpu_data.x86_capability[0] = cpuid_edx(1);
 #endif
 
+	if (xen_start_info->mod_start) {
+	    if (xen_start_info->flags & SIF_MOD_START_PFN)
+		initrd_start = PFN_PHYS(xen_start_info->mod_start);
+	    else
+		initrd_start = __pa(xen_start_info->mod_start);
+	}
+
 	/* Poke various useful things into boot_params */
 	boot_params.hdr.type_of_loader = (9 << 4) | 0;
-	boot_params.hdr.ramdisk_image = xen_start_info->mod_start
-		? __pa(xen_start_info->mod_start) : 0;
+	boot_params.hdr.ramdisk_image = initrd_start;
 	boot_params.hdr.ramdisk_size = xen_start_info->mod_len;
 	boot_params.hdr.cmd_line_ptr = __pa(xen_start_info->cmd_line);
 

arch/x86/xen/xen-head.S

@@ -124,6 +124,7 @@ NEXT_HYPERCALL(arch_6)
 	ELFNOTE(Xen, XEN_ELFNOTE_L1_MFN_VALID,
 		.quad _PAGE_PRESENT; .quad _PAGE_PRESENT)
 	ELFNOTE(Xen, XEN_ELFNOTE_SUSPEND_CANCEL, .long 1)
+	ELFNOTE(Xen, XEN_ELFNOTE_MOD_START_PFN,  .long 1)
 	ELFNOTE(Xen, XEN_ELFNOTE_HV_START_LOW,   _ASM_PTR __HYPERVISOR_VIRT_START)
 	ELFNOTE(Xen, XEN_ELFNOTE_PADDR_OFFSET,   _ASM_PTR 0)