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Date: Thu, 9 May 2024 00:00:23 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Mike Rapoport <rppt@kernel.org>
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Subject: Re: [POC][RFC][PATCH 0/2] pstore/mm/x86: Add wildcard memmap to map
 pstore consistently
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On Wed, 1 May 2024 18:30:40 +0300
Mike Rapoport <rppt@kernel.org> wrote:

> > So this will allocate the same physical location for every boot, if booting
> > the same kernel and having the same physical memory layout?  
> 
> Up to kaslr that might use that location for the kernel image.
> But it's the same as allocating from e820 after kaslr.
> 
> And, TBH, I don't have good ideas how to ensure the same physical location
> with randomization of the physical address of the kernel image.
>  

I tried this approach and it unfortunately picks a different physical
location every time :-(

So it is either adding to e820 tables or we create a new way to
allocate memory at early boot up.

Below is the patch I used.

-- Steve


diff --git a/include/linux/mm.h b/include/linux/mm.h
index b6bdaa18b9e9..74aaf0bcb363 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4204,4 +4204,6 @@ static inline bool pfn_is_unaccepted_memory(unsigned long pfn)
 	return range_contains_unaccepted_memory(paddr, paddr + PAGE_SIZE);
 }
 
+int memmap_named(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..3c015395d262 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2243,6 +2243,101 @@ void __init memblock_free_all(void)
 	pages = free_low_memory_core_early();
 	totalram_pages_add(pages);
 }
+/* For wildcard memory requests, have a table to find them later */
+#define MEMMAP_MAX_MAPS		8
+#define MEMMAP_NAME_SIZE	16
+struct memmap_map {
+	char			name[MEMMAP_NAME_SIZE];
+	unsigned long		start;
+	unsigned long		size;
+};
+static struct memmap_map memmap_list[MEMMAP_MAX_MAPS] __initdata;
+static int memmap_size				__initdata;
+
+/* Add wildcard region with a lookup name */
+static int __init memmap_add(u64 start, u64 size, const char *name)
+{
+	struct memmap_map *map;
+
+	if (!name || !name[0] || strlen(name) >= MEMMAP_NAME_SIZE)
+		return -EINVAL;
+
+	if (memmap_size >= MEMMAP_MAX_MAPS)
+		return -1;
+
+	map = &memmap_list[memmap_size++];
+	map->start = start;
+	map->size = size;
+	strcpy(map->name, name);
+	return 0;
+}
+
+/**
+ * memmap_named - Find a wildcard region with a given name
+ * @name: The name that is attached to a wildcard 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 __init memmap_named(const char *name, unsigned long *start, unsigned long *size)
+{
+	struct memmap_map *map;
+	int i;
+
+	for (i = 0; i < memmap_size; i++) {
+		map = &memmap_list[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 early_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 = memmap_add(start, size, p);
+	if (err) {
+		memblock_phys_free(start, size);
+		return err;
+	}
+
+	p += strlen(p);
+
+	return *p == '\0' ? 0: -EINVAL;
+}
+__setup("early_reserve_mem=", early_reserve_mem);
 
 #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK)
 static const char * const flagname[] = {