Hi Bhupesh,

-----Original Message-----
> This patch adds a common feature for archs (except arm64, for which
> similar support is added via subsequent patch) to retrieve
> 'MAX_PHYSMEM_BITS' from vmcoreinfo (if available).
> 
> I recently posted a kernel patch (see [0]) which appends
> 'MAX_PHYSMEM_BITS' to vmcoreinfo in the core code itself rather than
> in arch-specific code, so that user-space code can also benefit from
> this addition to the vmcoreinfo and use it as a standard way of
> determining 'SECTIONS_SHIFT' value in 'makedumpfile' utility.
> 
> This patch ensures backward compatibility for kernel versions in which
> 'MAX_PHYSMEM_BITS' is not available in vmcoreinfo.
> 
> [0]. http://lists.infradead.org/pipermail/kexec/2019-November/023960.html

This archive page appears gone..  I modified the commit message.
Please see comments below.

> 
> Cc: Kazuhito Hagio <[email protected]>
> Cc: John Donnelly <[email protected]>
> Cc: [email protected]
> Signed-off-by: Bhupesh Sharma <[email protected]>
> ---
>  arch/arm.c     |  8 +++++++-
>  arch/ia64.c    |  7 ++++++-
>  arch/ppc.c     |  8 +++++++-
>  arch/ppc64.c   | 49 ++++++++++++++++++++++++++++---------------------
>  arch/s390x.c   | 29 ++++++++++++++++++-----------
>  arch/sparc64.c |  9 +++++++--
>  arch/x86.c     | 34 ++++++++++++++++++++--------------
>  arch/x86_64.c  | 27 ++++++++++++++++-----------
>  8 files changed, 109 insertions(+), 62 deletions(-)
> 
> diff --git a/arch/arm.c b/arch/arm.c
> index af7442ac70bf..33536fc4dfc9 100644
> --- a/arch/arm.c
> +++ b/arch/arm.c
> @@ -81,7 +81,13 @@ int
>  get_machdep_info_arm(void)
>  {
>       info->page_offset = SYMBOL(_stext) & 0xffff0000UL;
> -     info->max_physmem_bits = _MAX_PHYSMEM_BITS;
> +
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
> +     else
> +             info->max_physmem_bits = _MAX_PHYSMEM_BITS;
> +
>       info->kernel_start = SYMBOL(_stext);
>       info->section_size_bits = _SECTION_SIZE_BITS;
> 
> diff --git a/arch/ia64.c b/arch/ia64.c
> index 6c33cc7c8288..fb44dda47172 100644
> --- a/arch/ia64.c
> +++ b/arch/ia64.c
> @@ -85,7 +85,12 @@ get_machdep_info_ia64(void)
>       }
> 
>       info->section_size_bits = _SECTION_SIZE_BITS;
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
> +
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
> +     else
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
> 
>       return TRUE;
>  }
> diff --git a/arch/ppc.c b/arch/ppc.c
> index 37c6a3b60cd3..ed9447427a30 100644
> --- a/arch/ppc.c
> +++ b/arch/ppc.c
> @@ -31,7 +31,13 @@ get_machdep_info_ppc(void)
>       unsigned long vmlist, vmap_area_list, vmalloc_start;
> 
>       info->section_size_bits = _SECTION_SIZE_BITS;
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
> +
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
> +     else
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
> +
>       info->page_offset = __PAGE_OFFSET;
> 
>       if (SYMBOL(_stext) != NOT_FOUND_SYMBOL)
> diff --git a/arch/ppc64.c b/arch/ppc64.c
> index 9d8f2525f608..a3984eebdced 100644
> --- a/arch/ppc64.c
> +++ b/arch/ppc64.c
> @@ -466,30 +466,37 @@ int
>  set_ppc64_max_physmem_bits(void)
>  {
>       long array_len = ARRAY_LENGTH(mem_section);
> -     /*
> -      * The older ppc64 kernels uses _MAX_PHYSMEM_BITS as 42 and the
> -      * newer kernels 3.7 onwards uses 46 bits.
> -      */
> -
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG ;
> -     if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> -             || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> -             return TRUE;
> -
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_3_7;
> -     if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> -             || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> -             return TRUE;
> 
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_4_19;
> -     if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> -             || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
>               return TRUE;
> +     } else {
> +             /*
> +              * The older ppc64 kernels uses _MAX_PHYSMEM_BITS as 42 and the
> +              * newer kernels 3.7 onwards uses 46 bits.
> +              */
> 
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_4_20;
> -     if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> -             || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> -             return TRUE;
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG ;
> +             if ((array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT_EXTREME()))
> +                             || (array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT())))
> +                     return TRUE;
> +
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_3_7;
> +             if ((array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT_EXTREME()))
> +                             || (array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT())))
> +                     return TRUE;
> +
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_4_19;
> +             if ((array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT_EXTREME()))
> +                             || (array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT())))
> +                     return TRUE;
> +
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_4_20;
> +             if ((array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT_EXTREME()))
> +                             || (array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT())))
> +                     return TRUE;
> +     }
> 
>       return FALSE;
>  }

That else block is not needed?  I will replace this hunk with:

--- a/arch/ppc64.c
+++ b/arch/ppc64.c
@@ -466,6 +466,13 @@ int
 set_ppc64_max_physmem_bits(void)
 {
        long array_len = ARRAY_LENGTH(mem_section);
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+               return TRUE;
+       }
+
        /*
         * The older ppc64 kernels uses _MAX_PHYSMEM_BITS as 42 and the
         * newer kernels 3.7 onwards uses 46 bits.


> diff --git a/arch/s390x.c b/arch/s390x.c
> index bf9d58e54fb7..4d17a783e5bd 100644
> --- a/arch/s390x.c
> +++ b/arch/s390x.c
> @@ -63,20 +63,27 @@ int
>  set_s390x_max_physmem_bits(void)
>  {
>       long array_len = ARRAY_LENGTH(mem_section);
> -     /*
> -      * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
> -      * newer kernels uses 46 bits.
> -      */
> 
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG ;
> -     if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> -             || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
>               return TRUE;
> +     } else {
> +             /*
> +              * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
> +              * newer kernels uses 46 bits.
> +              */
> 
> -     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_3_3;
> -     if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> -             || (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> -             return TRUE;
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG ;
> +             if ((array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT_EXTREME()))
> +                             || (array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT())))
> +                     return TRUE;
> +
> +             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_3_3;
> +             if ((array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT_EXTREME()))
> +                             || (array_len == (NR_MEM_SECTIONS() / 
> _SECTIONS_PER_ROOT())))
> +                     return TRUE;
> +     }
> 
>       return FALSE;
>  }

Ditto.

--- a/arch/s390x.c
+++ b/arch/s390x.c
@@ -63,6 +63,13 @@ int
 set_s390x_max_physmem_bits(void)
 {
        long array_len = ARRAY_LENGTH(mem_section);
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+               return TRUE;
+       }
+
        /*
         * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
         * newer kernels uses 46 bits.


> diff --git a/arch/sparc64.c b/arch/sparc64.c
> index 1cfaa854ce6d..b93a05bdfe59 100644
> --- a/arch/sparc64.c
> +++ b/arch/sparc64.c
> @@ -25,10 +25,15 @@ int get_versiondep_info_sparc64(void)
>  {
>       info->section_size_bits = _SECTION_SIZE_BITS;
> 
> -     if (info->kernel_version >= KERNEL_VERSION(3, 8, 13))
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
> +     else if (info->kernel_version >= KERNEL_VERSION(3, 8, 13))
>               info->max_physmem_bits = _MAX_PHYSMEM_BITS_L4;
> -     else {
> +     else
>               info->max_physmem_bits = _MAX_PHYSMEM_BITS_L3;
> +
> +     if (info->kernel_version < KERNEL_VERSION(3, 8, 13)) {
>               info->flag_vmemmap = TRUE;
>               info->vmemmap_start = VMEMMAP_BASE_SPARC64;
>               info->vmemmap_end = VMEMMAP_BASE_SPARC64 +
> diff --git a/arch/x86.c b/arch/x86.c
> index 3fdae93084b8..f1b43d4c8179 100644
> --- a/arch/x86.c
> +++ b/arch/x86.c
> @@ -72,21 +72,27 @@ get_machdep_info_x86(void)
>  {
>       unsigned long vmlist, vmap_area_list, vmalloc_start;
> 
> -     /* PAE */
> -     if ((vt.mem_flags & MEMORY_X86_PAE)
> -         || ((SYMBOL(pkmap_count) != NOT_FOUND_SYMBOL)
> -           && (SYMBOL(pkmap_count_next) != NOT_FOUND_SYMBOL)
> -           && ((SYMBOL(pkmap_count_next)-SYMBOL(pkmap_count))/sizeof(int))
> -           == 512)) {
> -             DEBUG_MSG("\n");
> -             DEBUG_MSG("PAE          : ON\n");
> -             vt.mem_flags |= MEMORY_X86_PAE;
> -             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_PAE;
> -     } else {
> -             DEBUG_MSG("\n");
> -             DEBUG_MSG("PAE          : OFF\n");
> -             info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
> +     else {
> +             /* PAE */
> +             if ((vt.mem_flags & MEMORY_X86_PAE)
> +                             || ((SYMBOL(pkmap_count) != NOT_FOUND_SYMBOL)
> +                                     && (SYMBOL(pkmap_count_next) != 
> NOT_FOUND_SYMBOL)
> +                                     && 
> ((SYMBOL(pkmap_count_next)-SYMBOL(pkmap_count))/sizeof(int))
> +                                     == 512)) {
> +                     DEBUG_MSG("\n");
> +                     DEBUG_MSG("PAE          : ON\n");
> +                     vt.mem_flags |= MEMORY_X86_PAE;
> +                     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_PAE;
> +             } else {
> +                     DEBUG_MSG("\n");
> +                     DEBUG_MSG("PAE          : OFF\n");
> +                     info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
> +             }

If we can get MAX_PHYSMEM_BITS from vmcoreinfo,
1. No "PAE : ON " or "PAE : OFF" debug message
2. No vt.mem_flags |= MEMORY_X86_PAE if pkmap check is true.

The latter will not occur with MAX_PHYSMEM_BITS in vmcoreinfo,
but for simplicity, I'd like to replace the hunk with the following.

--- a/arch/x86.c
+++ b/arch/x86.c
@@ -87,6 +87,11 @@ get_machdep_info_x86(void)
                DEBUG_MSG("PAE          : OFF\n");
                info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
        }
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+
        info->page_offset = __PAGE_OFFSET;
 
        if (SYMBOL(_stext) == NOT_FOUND_SYMBOL) {



>       }
> +
>       info->page_offset = __PAGE_OFFSET;
> 
>       if (SYMBOL(_stext) == NOT_FOUND_SYMBOL) {
> diff --git a/arch/x86_64.c b/arch/x86_64.c
> index b5e295452964..10eed83df655 100644
> --- a/arch/x86_64.c
> +++ b/arch/x86_64.c
> @@ -268,17 +268,22 @@ get_machdep_info_x86_64(void)
>  int
>  get_versiondep_info_x86_64(void)
>  {
> -     /*
> -      * On linux-2.6.26, MAX_PHYSMEM_BITS is changed to 44 from 40.
> -      */
> -     if (info->kernel_version < KERNEL_VERSION(2, 6, 26))
> -             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG;
> -     else if (info->kernel_version < KERNEL_VERSION(2, 6, 31))
> -             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_2_6_26;
> -     else if(check_5level_paging())
> -             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_5LEVEL;
> -     else
> -             info->max_physmem_bits  = _MAX_PHYSMEM_BITS_2_6_31;
> +     /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
> +     if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
> +             info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
> +     } else {
> +             /*
> +              * On linux-2.6.26, MAX_PHYSMEM_BITS is changed to 44 from 40.
> +              */
> +             if (info->kernel_version < KERNEL_VERSION(2, 6, 26))
> +                     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG;
> +             else if (info->kernel_version < KERNEL_VERSION(2, 6, 31))
> +                     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_2_6_26;
> +             else if(check_5level_paging())
> +                     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_5LEVEL;
> +             else
> +                     info->max_physmem_bits  = _MAX_PHYSMEM_BITS_2_6_31;
> +     }

Ditto.

--- a/arch/x86_64.c
+++ b/arch/x86_64.c
@@ -268,10 +268,10 @@ get_machdep_info_x86_64(void)
 int
 get_versiondep_info_x86_64(void)
 {
-       /*
-        * On linux-2.6.26, MAX_PHYSMEM_BITS is changed to 44 from 40.
-        */
-       if (info->kernel_version < KERNEL_VERSION(2, 6, 26))
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+       else if (info->kernel_version < KERNEL_VERSION(2, 6, 26))
                info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG;
        else if (info->kernel_version < KERNEL_VERSION(2, 6, 31))
                info->max_physmem_bits  = _MAX_PHYSMEM_BITS_2_6_26;

> 
>       if (!get_page_offset_x86_64())
>               return FALSE;
> --
> 2.26.2



So I modified the above hunks, could you check the following?
And I'm going to merge this patch separately from the 2/3 and 3/3 patch,
because those patches don't depend on this patch.


>From 93d32474eb18f955bb57cdc2b63dd2cb447a33fc Mon Sep 17 00:00:00 2001
From: Bhupesh Sharma <[email protected]>
Date: Thu, 10 Sep 2020 11:03:03 +0530
Subject: [PATCH] tree-wide: Retrieve MAX_PHYSMEM_BITS from vmcoreinfo

Add a common feature for architectures (except arm64, for which
similar support is added via a subsequent patch) to retrieve
MAX_PHYSMEM_BITS from vmcoreinfo, which was added by kernel commit
1d50e5d0c505 ("crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS'
to vmcoreinfo").  This makes makedumpfile adaptable for future
MAX_PHYSMEM_BITS changes.

Also ensure backward compatibility for kernel versions in which
MAX_PHYSMEM_BITS is not available in vmcoreinfo.

Signed-off-by: Bhupesh Sharma <[email protected]>
Signed-off-by: Kazuhito Hagio <[email protected]>
---
 arch/arm.c     | 8 +++++++-
 arch/ia64.c    | 7 ++++++-
 arch/ppc.c     | 8 +++++++-
 arch/ppc64.c   | 7 +++++++
 arch/s390x.c   | 7 +++++++
 arch/sparc64.c | 9 +++++++--
 arch/x86.c     | 5 +++++
 arch/x86_64.c  | 8 ++++----
 8 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/arch/arm.c b/arch/arm.c
index af7442ac70bf..33536fc4dfc9 100644
--- a/arch/arm.c
+++ b/arch/arm.c
@@ -81,7 +81,13 @@ int
 get_machdep_info_arm(void)
 {
        info->page_offset = SYMBOL(_stext) & 0xffff0000UL;
-       info->max_physmem_bits = _MAX_PHYSMEM_BITS;
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+       else
+               info->max_physmem_bits = _MAX_PHYSMEM_BITS;
+
        info->kernel_start = SYMBOL(_stext);
        info->section_size_bits = _SECTION_SIZE_BITS;
 
diff --git a/arch/ia64.c b/arch/ia64.c
index 6c33cc7c8288..fb44dda47172 100644
--- a/arch/ia64.c
+++ b/arch/ia64.c
@@ -85,7 +85,12 @@ get_machdep_info_ia64(void)
        }
 
        info->section_size_bits = _SECTION_SIZE_BITS;
-       info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+       else
+               info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
 
        return TRUE;
 }
diff --git a/arch/ppc.c b/arch/ppc.c
index 37c6a3b60cd3..ed9447427a30 100644
--- a/arch/ppc.c
+++ b/arch/ppc.c
@@ -31,7 +31,13 @@ get_machdep_info_ppc(void)
        unsigned long vmlist, vmap_area_list, vmalloc_start;
 
        info->section_size_bits = _SECTION_SIZE_BITS;
-       info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+       else
+               info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
+
        info->page_offset = __PAGE_OFFSET;
 
        if (SYMBOL(_stext) != NOT_FOUND_SYMBOL)
diff --git a/arch/ppc64.c b/arch/ppc64.c
index 9d8f2525f608..5e70acb51aba 100644
--- a/arch/ppc64.c
+++ b/arch/ppc64.c
@@ -466,6 +466,13 @@ int
 set_ppc64_max_physmem_bits(void)
 {
        long array_len = ARRAY_LENGTH(mem_section);
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+               return TRUE;
+       }
+
        /*
         * The older ppc64 kernels uses _MAX_PHYSMEM_BITS as 42 and the
         * newer kernels 3.7 onwards uses 46 bits.
diff --git a/arch/s390x.c b/arch/s390x.c
index bf9d58e54fb7..c4fed6f3bbd0 100644
--- a/arch/s390x.c
+++ b/arch/s390x.c
@@ -63,6 +63,13 @@ int
 set_s390x_max_physmem_bits(void)
 {
        long array_len = ARRAY_LENGTH(mem_section);
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER) {
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+               return TRUE;
+       }
+
        /*
         * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
         * newer kernels uses 46 bits.
diff --git a/arch/sparc64.c b/arch/sparc64.c
index 1cfaa854ce6d..b93a05bdfe59 100644
--- a/arch/sparc64.c
+++ b/arch/sparc64.c
@@ -25,10 +25,15 @@ int get_versiondep_info_sparc64(void)
 {
        info->section_size_bits = _SECTION_SIZE_BITS;
 
-       if (info->kernel_version >= KERNEL_VERSION(3, 8, 13))
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+       else if (info->kernel_version >= KERNEL_VERSION(3, 8, 13))
                info->max_physmem_bits = _MAX_PHYSMEM_BITS_L4;
-       else {
+       else
                info->max_physmem_bits = _MAX_PHYSMEM_BITS_L3;
+
+       if (info->kernel_version < KERNEL_VERSION(3, 8, 13)) {
                info->flag_vmemmap = TRUE;
                info->vmemmap_start = VMEMMAP_BASE_SPARC64;
                info->vmemmap_end = VMEMMAP_BASE_SPARC64 +
diff --git a/arch/x86.c b/arch/x86.c
index 3fdae93084b8..7899329c821f 100644
--- a/arch/x86.c
+++ b/arch/x86.c
@@ -87,6 +87,11 @@ get_machdep_info_x86(void)
                DEBUG_MSG("PAE          : OFF\n");
                info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
        }
+
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+
        info->page_offset = __PAGE_OFFSET;
 
        if (SYMBOL(_stext) == NOT_FOUND_SYMBOL) {
diff --git a/arch/x86_64.c b/arch/x86_64.c
index b5e295452964..58b5c0b7af40 100644
--- a/arch/x86_64.c
+++ b/arch/x86_64.c
@@ -268,10 +268,10 @@ get_machdep_info_x86_64(void)
 int
 get_versiondep_info_x86_64(void)
 {
-       /*
-        * On linux-2.6.26, MAX_PHYSMEM_BITS is changed to 44 from 40.
-        */
-       if (info->kernel_version < KERNEL_VERSION(2, 6, 26))
+       /* Check if we can get MAX_PHYSMEM_BITS from vmcoreinfo */
+       if (NUMBER(MAX_PHYSMEM_BITS) != NOT_FOUND_NUMBER)
+               info->max_physmem_bits = NUMBER(MAX_PHYSMEM_BITS);
+       else if (info->kernel_version < KERNEL_VERSION(2, 6, 26))
                info->max_physmem_bits  = _MAX_PHYSMEM_BITS_ORIG;
        else if (info->kernel_version < KERNEL_VERSION(2, 6, 31))
                info->max_physmem_bits  = _MAX_PHYSMEM_BITS_2_6_26;
-- 
1.8.3.1


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