[PATCH 01/15] mm,memblock: Add support for scratch memory

@@ -42,6 +42,10 @@ extern unsigned long long max_possible_pfn;
  * kernel resource tree.
  * @MEMBLOCK_RSRV_NOINIT: memory region for which struct pages are
  * not initialized (only for reserved regions).
+ * @MEMBLOCK_SCRATCH: memory region that kexec can pass to the next kernel in
+ * handover mode. During early boot, we do not know about all memory reservations
+ * yet, so we get scratch memory from the previous kernel that we know is good
+ * to use. It is the only memory that allocations may happen from in this phase.
  */
 enum memblock_flags {
 	MEMBLOCK_NONE		= 0x0,	/* No special request */

@@ -50,6 +54,7 @@ enum memblock_flags {
 	MEMBLOCK_NOMAP		= 0x4,	/* don't add to kernel direct mapping */
 	MEMBLOCK_DRIVER_MANAGED = 0x8,	/* always detected via a driver */
 	MEMBLOCK_RSRV_NOINIT	= 0x10,	/* don't initialize struct pages */
+	MEMBLOCK_SCRATCH	= 0x20,	/* scratch memory for kexec handover */
 };
 
 /**

@@ -129,6 +134,8 @@ int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
 int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t size);
+int memblock_mark_scratch(phys_addr_t base, phys_addr_t size);
+int memblock_clear_scratch(phys_addr_t base, phys_addr_t size);
 
 void memblock_free_all(void);
 void memblock_free(void *ptr, size_t size);

@@ -273,6 +280,11 @@ static inline bool memblock_is_driver_managed(struct memblock_region *m)
 	return m->flags & MEMBLOCK_DRIVER_MANAGED;
 }
 
+static inline bool memblock_is_scratch(struct memblock_region *m)
+{
+	return m->flags & MEMBLOCK_SCRATCH;
+}
+
 int memblock_search_pfn_nid(unsigned long pfn, unsigned long *start_pfn,
 			    unsigned long  *end_pfn);
 void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,

@@ -610,5 +622,12 @@ static inline void early_memtest(phys_addr_t start, phys_addr_t end) { }
 static inline void memtest_report_meminfo(struct seq_file *m) { }
 #endif
 
+#ifdef CONFIG_MEMBLOCK_SCRATCH
+void memblock_set_scratch_only(void);
+void memblock_clear_scratch_only(void);
+#else
+static inline void memblock_set_scratch_only(void) { }
+static inline void memblock_clear_scratch_only(void) { }
+#endif
 
 #endif /* _LINUX_MEMBLOCK_H */

@@ -513,6 +513,10 @@ config ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 config HAVE_MEMBLOCK_PHYS_MAP
 	bool
 
+# Enable memblock support for scratch memory which is needed for KHO
+config MEMBLOCK_SCRATCH
+	bool
+
 config HAVE_FAST_GUP
 	depends on MMU
 	bool

@@ -106,6 +106,13 @@ unsigned long min_low_pfn;
 unsigned long max_pfn;
 unsigned long long max_possible_pfn;
 
+#ifdef CONFIG_MEMBLOCK_SCRATCH
+/* When set to true, only allocate from MEMBLOCK_SCRATCH ranges */
+static bool scratch_only;
+#else
+#define scratch_only false
+#endif
+
 static struct memblock_region memblock_memory_init_regions[INIT_MEMBLOCK_MEMORY_REGIONS] __initdata_memblock;
 static struct memblock_region memblock_reserved_init_regions[INIT_MEMBLOCK_RESERVED_REGIONS] __initdata_memblock;
 #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP

@@ -168,6 +175,10 @@ bool __init_memblock memblock_has_mirror(void)
 
 static enum memblock_flags __init_memblock choose_memblock_flags(void)
 {
+	/* skip non-scratch memory for kho early boot allocations */
+	if (scratch_only)
+		return MEMBLOCK_SCRATCH;
+
 	return system_has_some_mirror ? MEMBLOCK_MIRROR : MEMBLOCK_NONE;
 }
 

@@ -643,7 +654,7 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
 #ifdef CONFIG_NUMA
 			WARN_ON(nid != memblock_get_region_node(rgn));
 #endif
-			WARN_ON(flags != rgn->flags);
+			WARN_ON(flags != (rgn->flags & ~MEMBLOCK_SCRATCH));
 			nr_new++;
 			if (insert) {
 				if (start_rgn == -1)

@@ -890,6 +901,18 @@ int __init_memblock memblock_physmem_add(phys_addr_t base, phys_addr_t size)
 }
 #endif
 
+#ifdef CONFIG_MEMBLOCK_SCRATCH
+__init_memblock void memblock_set_scratch_only(void)
+{
+	scratch_only = true;
+}
+
+__init_memblock void memblock_clear_scratch_only(void)
+{
+	scratch_only = false;
+}
+#endif
+
 /**
  * memblock_setclr_flag - set or clear flag for a memory region
  * @type: memblock type to set/clear flag for

@@ -1015,6 +1038,33 @@ int __init_memblock memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t
 				    MEMBLOCK_RSRV_NOINIT);
 }
 
+/**
+ * memblock_mark_scratch - Mark a memory region with flag MEMBLOCK_SCRATCH.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Only memory regions marked with %MEMBLOCK_SCRATCH will be considered for
+ * allocations during early boot with kexec handover.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_mark_scratch(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(&memblock.memory, base, size, 1, MEMBLOCK_SCRATCH);
+}
+
+/**
+ * memblock_clear_scratch - Clear flag MEMBLOCK_SCRATCH for a specified region.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_clear_scratch(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(&memblock.memory, base, size, 0, MEMBLOCK_SCRATCH);
+}
+
 static bool should_skip_region(struct memblock_type *type,
 			       struct memblock_region *m,
 			       int nid, int flags)

@@ -1046,6 +1096,14 @@ static bool should_skip_region(struct memblock_type *type,
 	if (!(flags & MEMBLOCK_DRIVER_MANAGED) && memblock_is_driver_managed(m))
 		return true;
 
+	/* In early alloc during kho, we can only consider scratch allocations */
+	if ((flags & MEMBLOCK_SCRATCH) && !memblock_is_scratch(m))
+		return true;
+
+	/* Leave scratch memory alone after scratch-only phase */
+	if (!(flags & MEMBLOCK_SCRATCH) && memblock_is_scratch(m))
+		return true;
+
 	return false;
 }
 

@@ -2211,6 +2269,7 @@ static const char * const flagname[] = {
 	[ilog2(MEMBLOCK_MIRROR)] = "MIRROR",
 	[ilog2(MEMBLOCK_NOMAP)] = "NOMAP",
 	[ilog2(MEMBLOCK_DRIVER_MANAGED)] = "DRV_MNG",
+	[ilog2(MEMBLOCK_SCRATCH)] = "SCRATCH",
 };
 
 static int memblock_debug_show(struct seq_file *m, void *private)