Commit 5ceeee75 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Dave Hansen
Browse files

x86/mm: Add a few comments 



It's a shame to hide useful comments in Changelogs, add some to the
code.

Shamelessly stolen from commit:

  c40a56a7 ("x86/mm/init: Remove freed kernel image areas from alias mapping")

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221110125544.460677011%40infradead.org
parent 80d0969a

arch/x86/mm/pat/set_memory.c

+20 −0
Original line number Diff line number Diff line
@@ -219,6 +219,23 @@ within_inclusive(unsigned long addr, unsigned long start, unsigned long end) 


#ifdef CONFIG_X86_64



/*

 * The kernel image is mapped into two places in the virtual address space

 * (addresses without KASLR, of course):

 *

 * 1. The kernel direct map (0xffff880000000000)

 * 2. The "high kernel map" (0xffffffff81000000)

 *

 * We actually execute out of #2. If we get the address of a kernel symbol, it

 * points to #2, but almost all physical-to-virtual translations point to #1.

 *

 * This is so that we can have both a directmap of all physical memory *and*

 * take full advantage of the the limited (s32) immediate addressing range (2G)

 * of x86_64.

 *

 * See Documentation/x86/x86_64/mm.rst for more detail.

 */



static inline unsigned long highmap_start_pfn(void)

{

	return __pa_symbol(_text) >> PAGE_SHIFT;
@@ -1626,6 +1643,9 @@ static int __change_page_attr(struct cpa_data *cpa, int primary) 


static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias);



/*

 * Check the directmap and "high kernel map" 'aliases'.

 */

static int cpa_process_alias(struct cpa_data *cpa)

{

	struct cpa_data alias_cpa;