x86/boot/e820: Rename early_reserve_e820() to e820__memblock_alloc() and document it

early_reserve_e820() is an early hack for kexec that does a limited fixup of the
mptable and passes it to the kexec kernel as if it was the real thing.

For this it needs to allocate memory - but no memory allocator is available yet
beyond the memblock allocator, so early_reserve_e820() is really a wrapper
around memblock_alloc() plus a hack to update the e820_table_firmware entries.

The name 'reserve' is really a bit of a misnomer, as 'reserved' memory typically
means memory completely inaccessible to the kernel - while here what we want to do
is a special RAM allocation for our own purposes and insert that as RAM_RESERVED.

Rename the function to e820__memblock_alloc_reserved() to better signal this dual
purpose, plus document it better, which was omitted when it was merged. The barely
comprehensible and cryptic comment:

  /*
   * pre allocated 4k and reserved it in memblock and e820_table_firmware
   */
  u64 __init e820__memblock_alloc_reserved(u64 size, u64 align)

... does not count as documentation, replace it with:

  /*
   * Allocate the requested number of bytes with the requsted alignment
   * and return (the physical address) to the caller. Also register this
   * range in the 'firmware' E820 table.
   *
   * This allows kexec to fake a new mptable, as if it came from the real
   * system.
   */
  u64 __init e820__memblock_alloc_reserved(u64 size, u64 align)

No change in functionality.

Cc: Alex Thorlton <athorlton@sgi.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Jackson <pj@sgi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 904ddb1343f2..93b5e3e5a3f0 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -734,16 +734,21 @@ core_initcall(e820_mark_nvs_memory);
 #endif
 
 /*
- * pre allocated 4k and reserved it in memblock and e820_table_firmware
+ * Allocate the requested number of bytes with the requsted alignment
+ * and return (the physical address) to the caller. Also register this
+ * range in the 'firmware' E820 table as a reserved range.
+ *
+ * This allows kexec to fake a new mptable, as if it came from the real
+ * system.
  */
-u64 __init early_reserve_e820(u64 size, u64 align)
+u64 __init e820__memblock_alloc_reserved(u64 size, u64 align)
 {
 	u64 addr;
 
 	addr = __memblock_alloc_base(size, align, MEMBLOCK_ALLOC_ACCESSIBLE);
 	if (addr) {
 		e820_update_range_firmware(addr, size, E820_RAM, E820_RESERVED);
-		pr_info("e820: update e820_table_firmware for early_reserve_e820\n");
+		pr_info("e820: update e820_table_firmware for e820__memblock_alloc_reserved()\n");
 		update_e820_table_firmware();
 	}