* [PATCH] x86: mm: Add missing comments for initial kernel direct mapping
@ 2013-05-09 15:57 Zhang Yanfei
2013-05-10 12:08 ` [tip:x86/urgent] x86/mm: " tip-bot for Zhang Yanfei
0 siblings, 1 reply; 2+ messages in thread
From: Zhang Yanfei @ 2013-05-09 15:57 UTC (permalink / raw)
To: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, Yinghai Lu, Andrew Morton
Cc: Yasuaki Ishimatsu, Konrad Rzeszutek Wilk, linux-kernel
From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
For some reason, comments below are lost:
- comments for init_range_memory_mapping()
- comments in init_mem_mapping that is helpful for reminding people
that the pagetable is setup top-down
The comments were written by Yinghai in his patch in
https://lkml.org/lkml/2012/11/28/620
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
---
arch/x86/mm/init.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index fdc5dca..fed9993 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -359,7 +359,17 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
}
/*
- * would have hole in the middle or ends, and only ram parts will be mapped.
+ * We need to iterate through E820 memory map and create direct mappings
+ * for only E820_RAM and E820_KERN_RESERVED regions. We cannot simply
+ * create direct mappings for all pfns from [0 to max_low_pfn) and
+ * [4GB to max_pfn) because of possible memory holes in high addresses
+ * that cannot be marked as UC by fixed/variable range MTRRs.
+ * Depending on the alignment of E820 ranges, this may possibly result
+ * in using smaller size (i.e. 4K instead of 2M or 1G) page tables.
+ *
+ * init_mem_mapping call init_range_memory_mapping with big range.
+ * That range would have hole in the middle or ends, and only ram parts
+ * will be mapped in init_range_memory_mapping.
*/
static unsigned long __init init_range_memory_mapping(
unsigned long r_start,
@@ -419,6 +429,13 @@ void __init init_mem_mapping(void)
max_pfn_mapped = 0; /* will get exact value next */
min_pfn_mapped = real_end >> PAGE_SHIFT;
last_start = start = real_end;
+
+ /*
+ * We start from the top (end of memory) and go to the bottom.
+ * The memblock_find_in_range gets us a block of RAM from the
+ * end of RAM in [min_pfn_mapped, max_pfn_mapped) as new pages
+ * for page table.
+ */
while (last_start > ISA_END_ADDRESS) {
if (last_start > step_size) {
start = round_down(last_start - 1, step_size);
--
1.8.1.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [tip:x86/urgent] x86/mm: Add missing comments for initial kernel direct mapping
2013-05-09 15:57 [PATCH] x86: mm: Add missing comments for initial kernel direct mapping Zhang Yanfei
@ 2013-05-10 12:08 ` tip-bot for Zhang Yanfei
0 siblings, 0 replies; 2+ messages in thread
From: tip-bot for Zhang Yanfei @ 2013-05-10 12:08 UTC (permalink / raw)
To: linux-tip-commits
Cc: linux-kernel, hpa, mingo, konrad.wilk, zhangyanfei, akpm,
isimatu.yasuaki, tglx
Commit-ID: cf8b166d5c1c89aad6c436a954fa40fd18a75bfb
Gitweb: http://git.kernel.org/tip/cf8b166d5c1c89aad6c436a954fa40fd18a75bfb
Author: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
AuthorDate: Thu, 9 May 2013 23:57:42 +0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 10 May 2013 12:00:35 +0200
x86/mm: Add missing comments for initial kernel direct mapping
Two sets of comments were lost during patch-series shuffling:
- comments for init_range_memory_mapping()
- comments in init_mem_mapping that is helpful for reminding people
that the pagetable is setup top-down
The comments were written by Yinghai in his patch in:
https://lkml.org/lkml/2012/11/28/620
This patch reintroduces them.
Originally-From: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/518BC776.7010506@gmail.com
[ Tidied it all up a bit. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/mm/init.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index fdc5dca..eaac174 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -359,7 +359,17 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
}
/*
- * would have hole in the middle or ends, and only ram parts will be mapped.
+ * We need to iterate through the E820 memory map and create direct mappings
+ * for only E820_RAM and E820_KERN_RESERVED regions. We cannot simply
+ * create direct mappings for all pfns from [0 to max_low_pfn) and
+ * [4GB to max_pfn) because of possible memory holes in high addresses
+ * that cannot be marked as UC by fixed/variable range MTRRs.
+ * Depending on the alignment of E820 ranges, this may possibly result
+ * in using smaller size (i.e. 4K instead of 2M or 1G) page tables.
+ *
+ * init_mem_mapping() calls init_range_memory_mapping() with big range.
+ * That range would have hole in the middle or ends, and only ram parts
+ * will be mapped in init_range_memory_mapping().
*/
static unsigned long __init init_range_memory_mapping(
unsigned long r_start,
@@ -419,6 +429,13 @@ void __init init_mem_mapping(void)
max_pfn_mapped = 0; /* will get exact value next */
min_pfn_mapped = real_end >> PAGE_SHIFT;
last_start = start = real_end;
+
+ /*
+ * We start from the top (end of memory) and go to the bottom.
+ * The memblock_find_in_range() gets us a block of RAM from the
+ * end of RAM in [min_pfn_mapped, max_pfn_mapped) used as new pages
+ * for page table.
+ */
while (last_start > ISA_END_ADDRESS) {
if (last_start > step_size) {
start = round_down(last_start - 1, step_size);
^ permalink raw reply related [flat|nested] 2+ messages in thread
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