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Date: Mon, 03 Jun 2024 19:33:31 -0400
From: Steven Rostedt <rostedt@goodmis.org>
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Cc: Masami Hiramatsu <mhiramat@kernel.org>,
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 Will Deacon <will@kernel.org>,
 Mike Rapoport <rppt@kernel.org>
Subject: [PATCH 1/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up
References: <20240603233330.801075898@goodmis.org>
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From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

In order to allow for requesting a memory region that can be used for
things like pstore on multiple machines where the memory layout is not the
same, add a new option to the kernel command line called "reserve_mem".

The format is:  reserve_mem=nn:align:name

Where it will find nn amount of memory at the given alignment of align.
The name field is to allow another subsystem to retrieve where the memory
was found. For example:

  reserve_mem=12M:4096:oops ramoops.mem_name=oops

Where ramoops.mem_name will tell ramoops that memory was reserved for it
via the reserve_mem option and it can find it by calling:

  if (reserve_mem_find_by_name("oops", &start, &size)) {
	// start holds the start address and size holds the size given

Link: https://lore.kernel.org/all/ZjJVnZUX3NZiGW6q@kernel.org/

Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/mm.h |  2 +
 mm/memblock.c      | 97 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9849dfda44d4..b4455cc02f2c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4263,4 +4263,6 @@ static inline bool pfn_is_unaccepted_memory(unsigned long pfn)
 void vma_pgtable_walk_begin(struct vm_area_struct *vma);
 void vma_pgtable_walk_end(struct vm_area_struct *vma);
 
+int reserve_mem_find_by_name(const char *name, unsigned long *start, unsigned long *size);
+
 #endif /* _LINUX_MM_H */
diff --git a/mm/memblock.c b/mm/memblock.c
index d09136e040d3..a8bf0ee9e2b4 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2244,6 +2244,103 @@ void __init memblock_free_all(void)
 	totalram_pages_add(pages);
 }
 
+/* Keep a table to reserve named memory */
+#define RESERVE_MEM_MAX_ENTRIES		8
+#define RESERVE_MEM_NAME_SIZE		16
+struct reserve_mem_table {
+	char			name[RESERVE_MEM_NAME_SIZE];
+	unsigned long		start;
+	unsigned long		size;
+};
+static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
+static int reserved_mem_count;
+
+/* Add wildcard region with a lookup name */
+static int __init reserved_mem_add(unsigned long start, unsigned long size,
+				   const char *name)
+{
+	struct reserve_mem_table *map;
+
+	if (!name || !name[0] || strlen(name) >= RESERVE_MEM_NAME_SIZE)
+		return -EINVAL;
+
+	if (reserved_mem_count >= RESERVE_MEM_MAX_ENTRIES)
+		return -1;
+
+	map = &reserved_mem_table[reserved_mem_count++];
+	map->start = start;
+	map->size = size;
+	strscpy(map->name, name);
+	return 0;
+}
+
+/**
+ * reserve_mem_find_by_name - Find reserved memory region with a given name
+ * @name: The name that is attached to a reserved memory region
+ * @start: If found, holds the start address
+ * @size: If found, holds the size of the address.
+ *
+ * Returns: 1 if found or 0 if not found.
+ */
+int reserve_mem_find_by_name(const char *name, unsigned long *start, unsigned long *size)
+{
+	struct reserve_mem_table *map;
+	int i;
+
+	for (i = 0; i < reserved_mem_count; i++) {
+		map = &reserved_mem_table[i];
+		if (!map->size)
+			continue;
+		if (strcmp(name, map->name) == 0) {
+			*start = map->start;
+			*size = map->size;
+			return 1;
+		}
+	}
+	return 0;
+}
+
+/*
+ * Parse early_reserve_mem=nn:align:name
+ */
+static int __init reserve_mem(char *p)
+{
+	phys_addr_t start, size, align;
+	char *oldp;
+	int err;
+
+	if (!p)
+		return -EINVAL;
+
+	oldp = p;
+	size = memparse(p, &p);
+	if (p == oldp)
+		return -EINVAL;
+
+	if (*p != ':')
+		return -EINVAL;
+
+	align = memparse(p+1, &p);
+	if (*p != ':')
+		return -EINVAL;
+
+	start = memblock_phys_alloc(size, align);
+	if (!start)
+		return -ENOMEM;
+
+	p++;
+	err = reserved_mem_add(start, size, p);
+	if (err) {
+		memblock_phys_free(start, size);
+		return err;
+	}
+
+	p += strlen(p);
+
+	return *p == '\0' ? 0: -EINVAL;
+}
+__setup("reserve_mem=", reserve_mem);
+
 #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK)
 static const char * const flagname[] = {
 	[ilog2(MEMBLOCK_HOTPLUG)] = "HOTPLUG",
-- 
2.43.0