On 26.08.25 07:25, Lorenzo Stoakes wrote:
On Mon, Aug 25, 2025 at 02:31:00PM +0200, David Hildenbrand wrote:
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 <david@xxxxxxxxxx>
---
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:
Out of interest do you know why this is happening? xtensa right? Does
xtensa not like CONFIG_DEBUG_VM?
We don't happen to include mmdebug.h in a xtensa configuration.
Briefly thought about using a BUILD_BUG_ON_INVALID(), but decided to
just drop it completely.
--
Cheers
David / dhildenb
