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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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