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Subject[RFC PATCH] x86_64/mm/boot: Fix kernel_ident_mapping_init() failure for kexec
Date
I found that the kdump is broken on linux-4.11.0-rc2+, probably
due to the 5level-paging feature that "#define p4d_present(p4d) 1",
as a result in ident_p4d_init(), it will go into ident_pud_init()
directly without allocating the new pud.

Looks like this patch can make it work again.

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Xunlei Pang <xlpang@redhat.com>
---
arch/x86/mm/ident_map.c | 22 ++++++++++------------
include/asm-generic/5level-fixup.h | 6 +++---
2 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
index 04210a2..d14bb52 100644
--- a/arch/x86/mm/ident_map.c
+++ b/arch/x86/mm/ident_map.c
@@ -97,22 +97,20 @@ int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
continue;
}

- p4d = (p4d_t *)info->alloc_pgt_page(info->context);
- if (!p4d)
- return -ENOMEM;
+ if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
+ p4d = (p4d_t *)info->alloc_pgt_page(info->context);
+ if (!p4d)
+ return -ENOMEM;
+ } else {
+ p4d = pgd;
+ }
+
result = ident_p4d_init(info, p4d, addr, next);
if (result)
return result;
- if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
+
+ if (IS_ENABLED(CONFIG_X86_5LEVEL))
set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
- } else {
- /*
- * With p4d folded, pgd is equal to p4d.
- * The pgd entry has to point to the pud page table in this case.
- */
- pud_t *pud = pud_offset(p4d, 0);
- set_pgd(pgd, __pgd(__pa(pud) | _KERNPG_TABLE));
- }
}

return 0;
diff --git a/include/asm-generic/5level-fixup.h b/include/asm-generic/5level-fixup.h
index b5ca82d..3131ada 100644
--- a/include/asm-generic/5level-fixup.h
+++ b/include/asm-generic/5level-fixup.h
@@ -17,9 +17,9 @@

#define p4d_alloc(mm, pgd, address) (pgd)
#define p4d_offset(pgd, start) (pgd)
-#define p4d_none(p4d) 0
-#define p4d_bad(p4d) 0
-#define p4d_present(p4d) 1
+#define p4d_none(p4d) pgd_none(p4d)
+#define p4d_bad(p4d) pgd_bad(p4d)
+#define p4d_present(p4d) pgd_present(p4d)
#define p4d_ERROR(p4d) do { } while (0)
#define p4d_clear(p4d) pgd_clear(p4d)
#define p4d_val(p4d) pgd_val(p4d)
--
1.8.3.1
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