crash: export PAGE_UNACCEPTED_MAPCOUNT_VALUE to vmcoreinfo

On Intel TDX guest, unaccepted memory is unusable free memory which is not
managed by buddy, until it's accepted by guest.  Before that, it cannot be
accessed by the first kernel as well as the kexec'ed kernel.  The kexec'ed
kernel will skip these pages and fill in zero data for the reader of
vmcore.

The dump tool like makedumpfile creates a page descriptor (size 24 bytes)
for each non-free page, including zero data page, but it will not create
descriptor for free pages.  If it is not able to distinguish these
unaccepted pages with zero data pages, a certain amount of space will be
wasted in proportion (~1/170).  In fact, as a special kind of free page
the unaccepted pages should be excluded, like the real free pages.

Export the page type PAGE_UNACCEPTED_MAPCOUNT_VALUE to vmcoreinfo, so that
dump tool can identify whether a page is unaccepted.

[[email protected]: fix docs: "Title underline too short" warning]
  Link: https://lore.kernel.org/all/[email protected]/
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lore.kernel.org/all/[email protected]/
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Zhiquan Li <[email protected]>
Reviewed-by: Kirill A. Shutemov <[email protected]>
Acked-by: Baoquan He <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Zhiquan Li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: zhiquan1-li

Documentation/admin-guide/kdump/vmcoreinfo.rst

@@ -331,8 +331,8 @@ PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision|PG_head_mask|P
 Page attributes. These flags are used to filter various unnecessary for
 dumping pages.
 
-PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)
------------------------------------------------------------------------------
+PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_unaccepted)
+-------------------------------------------------------------------------------------------------------------------------
 
 More page attributes. These flags are used to filter various unnecessary for
 dumping pages.

kernel/vmcore_info.c

@@ -210,6 +210,10 @@ static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_NUMBER(PAGE_HUGETLB_MAPCOUNT_VALUE);
 #define PAGE_OFFLINE_MAPCOUNT_VALUE	(PGTY_offline << 24)
 	VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE);
+#ifdef CONFIG_UNACCEPTED_MEMORY
+#define PAGE_UNACCEPTED_MAPCOUNT_VALUE	(PGTY_unaccepted << 24)
+	VMCOREINFO_NUMBER(PAGE_UNACCEPTED_MAPCOUNT_VALUE);
+#endif
 
 #ifdef CONFIG_KALLSYMS
 	VMCOREINFO_SYMBOL(kallsyms_names);