[Patch] x86, mm: fix the size calculation of mapping tables

[Patch] x86, mm: fix the size calculation of mapping tables

[xiyou.wangcong]

For machine enables PSE, the first 2/4M memory region still uses
4K pages, so needs more PTEs in this case, but find_early_table_space()
doesn't count this. This patch fixes it.

Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: ianfang.cn@gmail.com
Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>

---
 arch/x86/mm/init.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 6cabf65..2e92fdc 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -30,8 +30,14 @@ int direct_gbpages
 #endif
 ;
 
-static void __init find_early_table_space(unsigned long end, int use_pse,
-					  int use_gbpages)
+struct map_range {
+	unsigned long start;
+	unsigned long end;
+	unsigned page_size_mask;
+};
+
+static void __init find_early_table_space(struct map_range *mr, unsigned long end,
+					  int use_pse, int use_gbpages)
 {
 	unsigned long puds, pmds, ptes, tables, start = 0, good_end = end;
 	phys_addr_t base;
@@ -56,6 +62,9 @@ static void __init find_early_table_space(unsigned long end, int use_pse,
 #ifdef CONFIG_X86_32
 		extra += PMD_SIZE;
 #endif
+		/* The first 2/4M doesn't use large pages. */
+		extra += mr->end - mr->start;
+
 		ptes = (extra + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	} else
 		ptes = (end + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -85,12 +94,6 @@ void __init native_pagetable_reserve(u64 start, u64 end)
 	memblock_reserve(start, end - start);
 }
 
-struct map_range {
-	unsigned long start;
-	unsigned long end;
-	unsigned page_size_mask;
-};
-
 #ifdef CONFIG_X86_32
 #define NR_RANGE_MR 3
 #else /* CONFIG_X86_64 */
@@ -262,7 +265,7 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 	 * nodes are discovered.
 	 */
 	if (!after_bootmem)
-		find_early_table_space(end, use_pse, use_gbpages);
+		find_early_table_space(&mr[0], end, use_pse, use_gbpages);
 
 	for (i = 0; i < nr_range; i++)
 		ret = kernel_physical_mapping_init(mr[i].start, mr[i].end,

Re: [Patch] x86, mm: fix the size calculation of mapping tables

[Ingo Molnar]

* xiyou.wangcong@gmail.com <xiyou.wangcong@gmail.com> wrote:

> For machine enables PSE, the first 2/4M memory region still uses
> 4K pages, so needs more PTEs in this case, but find_early_table_space()
> doesn't count this. This patch fixes it.
> 
> Cc: Yinghai Lu <yinghai@kernel.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: ianfang.cn@gmail.com
> Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>

What were the symptoms of this bug - or have you found it via 
review only?

Thanks,

	Ingo