Re: [PATCH v5 1/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up
From: Mike Rapoport <rppt@kernel.org>
Date: 2024-06-13 06:02:47
Also in:
linux-hardening, linux-mm, lkml
On Wed, Jun 12, 2024 at 08:34:36PM -0400, Steven Rostedt wrote:
quoted hunk ↗ jump to hunk
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 This is typically used for systems that do not wipe the RAM, and this command line will try to reserve the same physical memory on soft reboots. Note, it is not guaranteed to be the same location. For example, if KASLR places the kernel at the location of where the RAM reservation was from a previous boot, the new reservation will be at a different location. Any subsystem using this feature must add a way to verify that the contents of the physical memory is from a previous boot, as there may be cases where the memory will not be located at the same location. Not all systems may work either. There could be bit flips if the reboot goes through the BIOS. Using kexec to reboot the machine is likely to have better results in such cases. Link: https://lore.kernel.org/all/ZjJVnZUX3NZiGW6q@kernel.org/ (local) Suggested-by: Mike Rapoport <rppt@kernel.org> Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> --- Changes since v4: https://lore.kernel.org/linux-trace-kernel/20240611215801.443593152@goodmis.org (local) - 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 "<=") .../admin-guide/kernel-parameters.txt | 20 +++ include/linux/mm.h | 2 + mm/memblock.c | 117 ++++++++++++++++++ 3 files changed, 139 insertions(+)diff --git a/mm/memblock.c b/mm/memblock.c index d09136e040d3..739d106a9165 100644 --- a/mm/memblock.c +++ b/mm/memblock.c
...
+/*
+ * Parse reserve_mem=nn:align:name
+ */
+static int __init reserve_mem(char *p)
+{
+ phys_addr_t start, size, align;
+ char *name;
+ char *oldp;
+ 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)
+ return -EINVAL;
+
+ if (*p != ':')
+ return -EINVAL;
+
+ align = memparse(p+1, &p);
+ if (*p != ':')
+ return -EINVAL;
+
+ /*
+ * 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)
+ align = SMP_CACHE_BYTES;
+
+ name = p + 1;
+ 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 */
+ for (p = name; *p; p++) {
+ if (!isspace(*p))
+ break;
+ }
+ 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;I'd prefer another variable here rather than size. Will be more robust IMO.
+
+ start = memblock_phys_alloc(size, align);
+ if (!start)
+ return -ENOMEM;
+
+ reserved_mem_add(start, size, name);
+
+ return 0;
+}
+__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
-- Sincerely yours, Mike.