Hi Vivek,

On Thu, 2014-09-25 at 14:28 -0400, Vivek Goyal wrote:

On Thu, Sep 25, 2014 at 12:23:27AM +0000, Geoff Levand wrote:
[..]

quoted

+void machine_kexec(struct kimage *image)
+{
+	phys_addr_t reboot_code_buffer_phys;
+	void *reboot_code_buffer;
+
+	BUG_ON(num_online_cpus() > 1);
+
+	kexec_kimage_head = image->head;
+
+	reboot_code_buffer_phys = page_to_phys(image->control_code_page);
+	reboot_code_buffer = phys_to_virt(reboot_code_buffer_phys);
+
+	/*
+	 * Copy relocate_new_kernel to the reboot_code_buffer for use
+	 * after the kernel is shut down.
+	 */
+
+	memcpy(reboot_code_buffer, relocate_new_kernel,
+		relocate_new_kernel_size);
+
+	/* Flush the reboot_code_buffer in preparation for its execution. */
+
+	__flush_dcache_area(reboot_code_buffer, relocate_new_kernel_size);
+
+	/* Flush the kimage list. */
+
+	kexec_list_walk(NULL, image->head, kexec_list_flush_cb);
+
+	pr_info("Bye!\n");
+
+	/* Disable all DAIF exceptions. */
+	
+	asm volatile ("msr daifset, #0xf" : : : "memory");
+
+	soft_restart(reboot_code_buffer_phys);

So what is soft_restart() functionality in arm64?

soft_restart() basically turns off the MMU and data caches, then jumps
to the address passed to it, reboot_code_buffer_phys here.
 

Looks like it switches to identity mapped page tables and that seems
to be the reason that you are not preparing identity mapped page
tables in kexec code. I am wondering I how do you make sure that once
kexec is swapping pages (putting new kernel's pages to its destination)
at that time these identity page will not be overwritten?

I am assuming that you are jumping to purgatory with paging enabled
and whole of the memory identity mapped.

The identity map is just used to turn off the MMU.  soft_restart() is in
that identity mapping, and once it shuts off the MMU it jumps to the
physical address of relocate_kernel, which uses physical addressing to
do the copy.

I am also curious to know what are different entry points arm64
kernel image supports and which one are you using by default.

The arm64 kernel as a single entry, the start of the image.  See
Documentation/arm64/booting.txt.

-Geoff