On 11.08.25 13:26, David Hildenbrand wrote:
print_bad_pte() looks like something that should actually be a WARN
or similar, but historically it apparently has proven to be useful to
detect corruption of page tables even on production systems -- report
the issue and keep the system running to make it easier to actually detect
what is going wrong (e.g., multiple such messages might shed a light).
As we want to unify vm_normal_page_*() handling for PTE/PMD/PUD, we'll have
to take care of print_bad_pte() as well.
Let's prepare for using print_bad_pte() also for non-PTEs by adjusting the
implementation and renaming the function to print_bad_page_map().
Provide print_bad_pte() as a simple wrapper.
Document the implicit locking requirements for the page table re-walk.
To make the function a bit more readable, factor out the ratelimit check
into is_bad_page_map_ratelimited() and place the printing of page
table content into __print_bad_page_map_pgtable(). We'll now dump
information from each level in a single line, and just stop the table
walk once we hit something that is not a present page table.
The report will now look something like (dumping pgd to pmd values):
[ 77.943408] BUG: Bad page map in process XXX pte:80000001233f5867
[ 77.944077] addr:00007fd84bb1c000 vm_flags:08100071 anon_vma: ...
[ 77.945186] pgd:10a89f067 p4d:10a89f067 pud:10e5a2067 pmd:105327067
Not using pgdp_get(), because that does not work properly on some arm
configs where pgd_t is an array. Note that we are dumping all levels
even when levels are folded for simplicity.
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
include/linux/pgtable.h | 19 ++++++++
mm/memory.c | 104 ++++++++++++++++++++++++++++++++--------
2 files changed, 103 insertions(+), 20 deletions(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index bff5c4241bf2e..33c84b38b7ec6 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1966,6 +1966,25 @@ enum pgtable_level {
PGTABLE_LEVEL_PGD,
};
+static inline const char *pgtable_level_to_str(enum pgtable_level level)
+{
+ switch (level) {
+ case PGTABLE_LEVEL_PTE:
+ return "pte";
+ case PGTABLE_LEVEL_PMD:
+ return "pmd";
+ case PGTABLE_LEVEL_PUD:
+ return "pud";
+ case PGTABLE_LEVEL_P4D:
+ return "p4d";
+ case PGTABLE_LEVEL_PGD:
+ return "pgd";
+ default:
+ VM_WARN_ON_ONCE(1);
+ return "unknown";
+ }
+}
One kernel config doesn't like the VM_WARN_ON_ONCE here, and I don't think we
really need it. @Andrew can you squash:
From 0b8f6cdfe2c9d96393e7da1772e82048e096a903 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <da...@redhat.com>
Date: Mon, 25 Aug 2025 14:25:59 +0200
Subject: [PATCH] fixup: mm/memory: convert print_bad_pte() to
print_bad_page_map()
Let's just drop the warning, it's highly unlikely that we ever run into
this, and if so, there is serious stuff going wrong elsewhere.
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
include/linux/pgtable.h | 1 -
1 file changed, 1 deletion(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 9f0329d45b1e1..94249e671a7e8 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1997,7 +1997,6 @@ static inline const char *pgtable_level_to_str(enum
pgtable_level level)
case PGTABLE_LEVEL_PGD:
return "pgd";
default:
- VM_WARN_ON_ONCE(1);
return "unknown";
}
}
--
2.50.1
--
Cheers
David / dhildenb
