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SubjectRe: [PATCH - resend] Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel(v1)
On Tue, Jan 12, 2010 at 08:30:31AM +0800, KAMEZAWA Hiroyuki wrote:
> On Mon, 11 Jan 2010 20:43:03 +0800
> Wu Fengguang <fengguang.wu@intel.com> wrote:
>
> > > > + /* if add to low memory, update max_low_pfn */
> > > > + if (unlikely(start_pfn < limit_low_pfn)) {
> > > > + if (end_pfn <= limit_low_pfn)
> > > > + max_low_pfn = end_pfn;
> > > > + else
> > > > + max_low_pfn = limit_low_pfn;
> > >
> > > X86_64 actually always set max_low_pfn=max_pfn, in setup_arch():
> > > [Zheng, Shaohui] there should be some misunderstanding, I read the
> > > code carefully, if the total memory is under 4G, it always
> > > max_low_pfn=max_pfn. If the total memory is larger than 4G,
> > > max_low_pfn means the end of low ram. It set
> >
> > > max_low_pfn = e820_end_of_low_ram_pfn();.
> >
> > The above line is very misleading.. In setup_arch(), it will be
> > overrode by the following block.
> >
>
> Hmmm....could you rewrite /dev/mem to use kernel/resource.c other than
> modifing e820 maps. ?
> Two reasons.
> - e820map is considerted to be stable, read-only after boot.
> - We don't need to add more x86 special codes.

Sure, here it is :)
---
x86: use the generic page_is_ram()
The generic resource based page_is_ram() works better with memory
hotplug/hotremove. So switch the x86 e820map based code to it.

CC: Andi Kleen <andi@firstfloor.org>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
arch/x86/include/asm/page_types.h | 1
arch/x86/mm/ioremap.c | 37 ----------------------------
kernel/resource.c | 17 ++++++++++++
3 files changed, 17 insertions(+), 38 deletions(-)
--- linux-mm.orig/arch/x86/include/asm/page_types.h 2010-01-12 10:31:01.000000000 +0800
+++ linux-mm/arch/x86/include/asm/page_types.h 2010-01-12 10:31:44.000000000 +0800
@@ -34,19 +34,18 @@

#ifdef CONFIG_X86_64
#include <asm/page_64_types.h>
#else
#include <asm/page_32_types.h>
#endif /* CONFIG_X86_64 */

#ifndef __ASSEMBLY__

-extern int page_is_ram(unsigned long pagenr);
extern int devmem_is_allowed(unsigned long pagenr);

extern unsigned long max_low_pfn_mapped;
extern unsigned long max_pfn_mapped;

extern unsigned long init_memory_mapping(unsigned long start,
unsigned long end);

extern void initmem_init(unsigned long start_pfn, unsigned long end_pfn,
--- linux-mm.orig/arch/x86/mm/ioremap.c 2010-01-12 10:31:01.000000000 +0800
+++ linux-mm/arch/x86/mm/ioremap.c 2010-01-12 10:31:44.000000000 +0800
@@ -18,55 +18,18 @@
#include <asm/e820.h>
#include <asm/fixmap.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/pgalloc.h>
#include <asm/pat.h>

#include "physaddr.h"

-int page_is_ram(unsigned long pagenr)
-{
- resource_size_t addr, end;
- int i;
-
- /*
- * A special case is the first 4Kb of memory;
- * This is a BIOS owned area, not kernel ram, but generally
- * not listed as such in the E820 table.
- */
- if (pagenr == 0)
- return 0;
-
- /*
- * Second special case: Some BIOSen report the PC BIOS
- * area (640->1Mb) as ram even though it is not.
- */
- if (pagenr >= (BIOS_BEGIN >> PAGE_SHIFT) &&
- pagenr < (BIOS_END >> PAGE_SHIFT))
- return 0;
-
- for (i = 0; i < e820.nr_map; i++) {
- /*
- * Not usable memory:
- */
- if (e820.map[i].type != E820_RAM)
- continue;
- addr = (e820.map[i].addr + PAGE_SIZE-1) >> PAGE_SHIFT;
- end = (e820.map[i].addr + e820.map[i].size) >> PAGE_SHIFT;
-
-
- if ((pagenr >= addr) && (pagenr < end))
- return 1;
- }
- return 0;
-}
-
/*
* Fix up the linear direct mapping of the kernel to avoid cache attribute
* conflicts.
*/
int ioremap_change_attr(unsigned long vaddr, unsigned long size,
unsigned long prot_val)
{
unsigned long nrpages = size >> PAGE_SHIFT;
int err;
--- linux-mm.orig/kernel/resource.c 2010-01-12 10:31:01.000000000 +0800
+++ linux-mm/kernel/resource.c 2010-01-12 10:31:44.000000000 +0800
@@ -298,18 +298,35 @@ int walk_system_ram_range(unsigned long
#endif

static int __is_ram(unsigned long pfn, unsigned long nr_pages, void *arg)
{
return 24;
}

int __attribute__((weak)) page_is_ram(unsigned long pfn)
{
+#ifdef CONFIG_X86
+ /*
+ * A special case is the first 4Kb of memory;
+ * This is a BIOS owned area, not kernel ram, but generally
+ * not listed as such in the E820 table.
+ */
+ if (pfn == 0)
+ return 0;
+
+ /*
+ * Second special case: Some BIOSen report the PC BIOS
+ * area (640->1Mb) as ram even though it is not.
+ */
+ if (pfn >= (BIOS_BEGIN >> PAGE_SHIFT) &&
+ pfn < (BIOS_END >> PAGE_SHIFT))
+ return 0;
+#endif
return 24 == walk_system_ram_range(pfn, 1, NULL, __is_ram);
}

/*
* Find empty slot in the resource tree given range and alignment.
*/
static int find_resource(struct resource *root, struct resource *new,
resource_size_t size, resource_size_t min,
resource_size_t max, resource_size_t align,


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