arm64: kexec: move relocation function setup

Currently, kernel relocation function is configured in machine_kexec()
at the time of kexec reboot by using control_code_page.

This operation, however, is more logical to be done during kexec_load,
and thus remove from reboot time. Move, setup of this function to
newly added machine_kexec_post_load().

Because once MMU is enabled, kexec control page will contain more than
relocation kernel, but also vector table, add pointer to the actual
function within this page arch.kern_reloc. Currently, it equals to the
beginning of page, we will add offsets later, when vector table is
added.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: James Morse <james.morse@arm.com>
Link: https://lore.kernel.org/r/20210125191923.1060122-10-pasha.tatashin@soleen.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/kexec.h

@@ -95,6 +95,7 @@ static inline void crash_post_resume(void) {}
 struct kimage_arch {
 	void *dtb;
 	phys_addr_t dtb_mem;
+	phys_addr_t kern_reloc;
 	/* Core ELF header buffer */
 	void *elf_headers;
 	unsigned long elf_headers_mem;

arch/arm64/kernel/machine_kexec.c

@@ -42,6 +42,7 @@ static void _kexec_image_info(const char *func, int line,
 	pr_debug("    start:       %lx\n", kimage->start);
 	pr_debug("    head:        %lx\n", kimage->head);
 	pr_debug("    nr_segments: %lu\n", kimage->nr_segments);
+	pr_debug("    kern_reloc: %pa\n", &kimage->arch.kern_reloc);
 
 	for (i = 0; i < kimage->nr_segments; i++) {
 		pr_debug("      segment[%lu]: %016lx - %016lx, 0x%lx bytes, %lu pages\n",
@@ -58,6 +59,22 @@ void machine_kexec_cleanup(struct kimage *kimage)
 	/* Empty routine needed to avoid build errors. */
 }
 
+int machine_kexec_post_load(struct kimage *kimage)
+{
+	void *reloc_code = page_to_virt(kimage->control_code_page);
+
+	memcpy(reloc_code, arm64_relocate_new_kernel,
+	       arm64_relocate_new_kernel_size);
+	kimage->arch.kern_reloc = __pa(reloc_code);
+
+	/* Flush the reloc_code in preparation for its execution. */
+	__flush_dcache_area(reloc_code, arm64_relocate_new_kernel_size);
+	flush_icache_range((uintptr_t)reloc_code, (uintptr_t)reloc_code +
+			   arm64_relocate_new_kernel_size);
+
+	return 0;
+}
+
 /**
  * machine_kexec_prepare - Prepare for a kexec reboot.
  *
@@ -143,8 +160,6 @@ static void kexec_segment_flush(const struct kimage *kimage)
  */
 void machine_kexec(struct kimage *kimage)
 {
-	phys_addr_t reboot_code_buffer_phys;
-	void *reboot_code_buffer;
 	bool in_kexec_crash = (kimage == kexec_crash_image);
 	bool stuck_cpus = cpus_are_stuck_in_kernel();
 
@@ -155,31 +170,8 @@ void machine_kexec(struct kimage *kimage)
 	WARN(in_kexec_crash && (stuck_cpus || smp_crash_stop_failed()),
 		"Some CPUs may be stale, kdump will be unreliable.\n");
 
-	reboot_code_buffer_phys = page_to_phys(kimage->control_code_page);
-	reboot_code_buffer = phys_to_virt(reboot_code_buffer_phys);
-
 	kexec_image_info(kimage);
 
-	/*
-	 * Copy arm64_relocate_new_kernel to the reboot_code_buffer for use
-	 * after the kernel is shut down.
-	 */
-	memcpy(reboot_code_buffer, arm64_relocate_new_kernel,
-		arm64_relocate_new_kernel_size);
-
-	/* Flush the reboot_code_buffer in preparation for its execution. */
-	__flush_dcache_area(reboot_code_buffer, arm64_relocate_new_kernel_size);
-
-	/*
-	 * Although we've killed off the secondary CPUs, we don't update
-	 * the online mask if we're handling a crash kernel and consequently
-	 * need to avoid flush_icache_range(), which will attempt to IPI
-	 * the offline CPUs. Therefore, we must use the __* variant here.
-	 */
-	__flush_icache_range((uintptr_t)reboot_code_buffer,
-			     (uintptr_t)reboot_code_buffer +
-			     arm64_relocate_new_kernel_size);
-
 	/* Flush the kimage list and its buffers. */
 	kexec_list_flush(kimage);
 
@@ -193,7 +185,7 @@ void machine_kexec(struct kimage *kimage)
 
 	/*
 	 * cpu_soft_restart will shutdown the MMU, disable data caches, then
-	 * transfer control to the reboot_code_buffer which contains a copy of
+	 * transfer control to the kern_reloc which contains a copy of
 	 * the arm64_relocate_new_kernel routine.  arm64_relocate_new_kernel
 	 * uses physical addressing to relocate the new image to its final
 	 * position and transfers control to the image entry point when the
@@ -203,7 +195,7 @@ void machine_kexec(struct kimage *kimage)
 	 * userspace (kexec-tools).
 	 * In kexec_file case, the kernel starts directly without purgatory.
 	 */
-	cpu_soft_restart(reboot_code_buffer_phys, kimage->head, kimage->start,
+	cpu_soft_restart(kimage->arch.kern_reloc, kimage->head, kimage->start,
 			 kimage->arch.dtb_mem);
 
 	BUG(); /* Should never get here. */