@@ -2256,22 +2256,15 @@ 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(phys_addr_t start, phys_addr_t size,
+static void __init reserved_mem_add(phys_addr_t start, phys_addr_t 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;
}
/**
@@ -2280,6 +2273,8 @@ static int __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
* @start: If found, holds the start address
* @size: If found, holds the size of the address.
*
+ * @start and @size are only updated if @name is found.
+ *
* Returns: 1 if found or 0 if not found.
*/
int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)
@@ -2309,11 +2304,15 @@ static int __init reserve_mem(char *p)
phys_addr_t start, size, align;
char *name;
char *oldp;
- int err;
+ int len;
if (!p)
return -EINVAL;
+ /* Check if there's room for more reserved memory */
+ if (reserved_mem_count >= RESERVE_MEM_MAX_ENTRIES)
+ return -EBUSY;
+
oldp = p;
size = memparse(p, &p);
if (!size || p == oldp)
@@ -2330,11 +2329,14 @@ static int __init reserve_mem(char *p)
* memblock_phys_alloc() doesn't like a zero size align,
* but it is OK for this command to have it.
*/
- if (align <= SMP_CACHE_BYTES)
+ if (align < SMP_CACHE_BYTES)
align = SMP_CACHE_BYTES;
name = p + 1;
- if (!strlen(name))
+ len = strlen(name);
+
+ /* name needs to have length but not too big */
+ if (!len || len >= RESERVE_MEM_NAME_SIZE)
return -EINVAL;
/* Make sure that name has text */
@@ -2345,15 +2347,15 @@ static int __init reserve_mem(char *p)
if (!*p)
return -EINVAL;
+ /* Make sure the name is not already used (size is only updated if found) */
+ if (reserve_mem_find_by_name(name, &start, &size))
+ return -EBUSY;
+
start = memblock_phys_alloc(size, align);
if (!start)
return -ENOMEM;
- err = reserved_mem_add(start, size, name);
- if (err) {
- memblock_phys_free(start, size);
- return err;
- }
+ reserved_mem_add(start, size, name);
return 0;
}
Reserve unspecified location of physical memory from kernel command line Background: In ChromeOS, we have 1 MB of pstore ramoops reserved so that we can extract dmesg output and some other information when a crash happens in the field. (This is only done when the user selects "Allow Google to collect data for improving the system"). But there are cases when there's a bug that requires more data to be retrieved to figure out what is happening. We would like to increase the pstore size, either temporarily, or maybe even permanently. The pstore on these devices are at a fixed location in RAM (as the RAM is not cleared on soft reboots nor crashes). The location is chosen by the BIOS (coreboot) and passed to the kernel via ACPI tables on x86. There's a driver that queries for this to initialize the pstore for ChromeOS: See drivers/platform/chrome/chromeos_pstore.c Problem: The problem is that, even though there's a process to change the kernel on these systems, and is done regularly to install updates, the firmware is updated much less frequently. Choosing the place in RAM also takes special care, and may be in a different address for different boards. Updating the size via firmware is a large effort and not something that many are willing to do for a temporary pstore size change. Requirement: Need a way to reserve memory that will be at a consistent location for every boot, if the kernel and system are the same. Does not need to work if rebooting to a different kernel, or if the system can change the memory layout between boots. The reserved memory can not be an hard coded address, as the same kernel / command line needs to run on several different machines. The picked memory reservation just needs to be the same for a given machine, but may be different for different machines. Solution: The solution I have come up with is to introduce a new "reserve_mem=" kernel command line. This parameter takes the following format: reserve_mem=nn:align:label Where nn is the size of memory to reserve, the align is the alignment of that memory, and label is the way for other sub-systems to find that memory. This way the kernel command line could have: reserve_mem=12M:4096:oops ramoops.mem_name=oops At boot up, the kernel will search for 12 megabytes in usable memory regions with an alignment of 4096. It will start at the highest regions and work its way down (for those old devices that want access to lower address DMA). When it finds a region, it will save it off in a small table and mark it with the "oops" label. Then the pstore ramoops sub-system could ask for that memory and location, and it will map itself there. This prototype allows for 8 different mappings (which may be overkill, 4 is probably plenty) with 16 byte size to store the label. I have tested this and it works for us to solve the above problem. We can update the kernel and command line and increase the size of pstore without needing to update the firmware, or knowing every memory layout of each board. I only tested this locally, it has not been tested in the field. Changes since v4: https://lore.kernel.org/all/20240611215610.548854415@goodmis.org/ [ patch at bottom showing differences ] - Add all checks about reserve_mem before allocation. This means reserved_mem_add() is now a void function. - Check for name duplications. - Fix compare of align to SMP_CACHE_BYTES ("<" instead of "<=") Changes since v3: https://lore.kernel.org/all/20240611144911.327227285@goodmis.org/ - Changed table type of start and size from unsigned long to phys_addr_t (as well as the parameters to the functions that use them) - Changed old reference to "early_reserve_mem" to "reserve_mem" - Check before reservering memory: o Size is non-zero o name has text in it - If align is less than SMP_CACHE_BYTES, make it SMP_CACHE_BYTES - Remove the silly check of testing *p == '\0' after a p += strlen(p) Changes since v2: https://lore.kernel.org/all/20240606150143.876469296@goodmis.org/ - Fixed typo of "reserver" - Added EXPORT_SYMBOL_GPL() for reserve_mem_find_by_name() - Removed "built-in" from module description that was changed from v1. Changes since v1: https://lore.kernel.org/all/20240603233330.801075898@goodmis.org/ - Updated the change log of the first patch as well as added an entry into kernel-parameters.txt about how reserve_mem is for soft reboots and may not be reliable. Steven Rostedt (Google) (2): mm/memblock: Add "reserve_mem" to reserved named memory at boot up pstore/ramoops: Add ramoops.mem_name= command line option ---- Documentation/admin-guide/kernel-parameters.txt | 20 ++++ fs/pstore/ram.c | 14 +++ include/linux/mm.h | 2 + mm/memblock.c | 117 ++++++++++++++++++++++++ 4 files changed, 153 insertions(+)