x86/kexec: Copy control page into place in machine_kexec_prepare()

There's no need for this to wait until the actual machine_kexec() invocation;
future changes will need to make the control page read-only and executable,
so all writes should be completed before machine_kexec_prepare() returns.

Signed-off-by: David Woodhouse <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: dwmw2

arch/x86/kernel/machine_kexec_64.c

@@ -301,17 +301,16 @@ static void load_segments(void)
 
 int machine_kexec_prepare(struct kimage *image)
 {
-	unsigned long control_page;
+	void *control_page = page_address(image->control_code_page);
 	int result;
 
-	/* Calculate the offsets */
-	control_page = page_to_pfn(image->control_code_page) << PAGE_SHIFT;
-
 	/* Setup the identity mapped 64bit page table */
-	result = init_pgtable(image, control_page);
+	result = init_pgtable(image, __pa(control_page));
 	if (result)
 		return result;
 
+	__memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
+
 	return 0;
 }
 
@@ -363,7 +362,6 @@ void machine_kexec(struct kimage *image)
 	}
 
 	control_page = page_address(image->control_code_page);
-	__memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
 
 	page_list[PA_CONTROL_PAGE] = virt_to_phys(control_page);
 	page_list[VA_CONTROL_PAGE] = (unsigned long)control_page;