On Fri, Dec 22, 2023 at 07:35:54PM +0000, Alexander Graf wrote:

+/**
+ * kho_reserve_previous_mem - Adds all memory reservations into memblocks
+ * and moves us out of the scratch only phase. Must be called after page tables
+ * are initialized and memblock_allow_resize().
+ */
+void __init kho_reserve_previous_mem(void)
+{
+	void *mem_virt = __va(mem_phys);
+	int off, err;
+
+	if (!handover_phys || !mem_phys)
+		return;
+
+	/*
+	 * We reached here because we are running inside a working linear map
+	 * that allows us to resize memblocks dynamically. Use the chance and
+	 * populate the global fdt pointer
+	 */
+	fdt = __va(handover_phys);
+
+	off = fdt_path_offset(fdt, "/");
+	if (off < 0) {
+		fdt = NULL;
+		return;
+	}
+
+	err = fdt_node_check_compatible(fdt, off, "kho-v1");
+	if (err) {
+		pr_warn("KHO has invalid compatible, disabling.");

It looks like KHO preserved regions won't be reserved in this case.
Should KHO DT state be destroyed here to prevent KHO memory regions
reuse upon rollback?

+
+void __init kho_populate(phys_addr_t handover_dt_phys, phys_addr_t scratch_phys,
+			 u64 scratch_len, phys_addr_t mem_cache_phys,
+			 u64 mem_cache_len)
+{
+	void *handover_dt;
+
+	/* Determine the real size of the DT */
+	handover_dt = early_memremap(handover_dt_phys, sizeof(struct fdt_header));
+	if (!handover_dt) {
+		pr_warn("setup: failed to memremap kexec FDT (0x%llx)\n", handover_dt_phys);
+		return;
+	}
+
+	if (fdt_check_header(handover_dt)) {
+		pr_warn("setup: kexec handover FDT is invalid (0x%llx)\n", handover_dt_phys);
+		early_memunmap(handover_dt, PAGE_SIZE);
+		return;
+	}
+
+	handover_len = fdt_totalsize(handover_dt);
+	handover_phys = handover_dt_phys;
+
+	/* Reserve the DT so we can still access it in late boot */
+	memblock_reserve(handover_phys, handover_len);
+
+	/* Reserve the mem cache so we can still access it later */
+	memblock_reserve(mem_cache_phys, mem_cache_len);
+
+	/*
+	 * We pass a safe contiguous block of memory to use for early boot purporses from
+	 * the previous kernel so that we can resize the memblock array as needed.
+	 */
+	memblock_add(scratch_phys, scratch_len);
+
+	if (WARN_ON(memblock_mark_scratch(scratch_phys, scratch_len))) {
+		pr_err("Kexec failed to mark the scratch region. Disabling KHO.");
+		handover_len = 0;
+		handover_phys = 0;

Same question here: doesn't all the KHO state gets invalid in case of any
restoration error?