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@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";
+ }
+}
+
#endif /* !__ASSEMBLY__ */
#if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT)
diff --git a/mm/memory.c b/mm/memory.c
index 626caedce35e0..dc0107354d37b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -491,22 +491,8 @@ static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
add_mm_counter(mm, i, rss[i]);
}
-/*
- * This function is called to print an error when a bad pte
- * is found. For example, we might have a PFN-mapped pte in
- * a region that doesn't allow it.
- *
- * The calling function must still handle the error.
- */
-static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
- pte_t pte, struct page *page)
+static bool is_bad_page_map_ratelimited(void)
{
- pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
- p4d_t *p4d = p4d_offset(pgd, addr);
- pud_t *pud = pud_offset(p4d, addr);
- pmd_t *pmd = pmd_offset(pud, addr);
- struct address_space *mapping;
- pgoff_t index;
static unsigned long resume;
static unsigned long nr_shown;
static unsigned long nr_unshown;
@@ -518,7 +504,7 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
if (nr_shown == 60) {
if (time_before(jiffies, resume)) {
nr_unshown++;
- return;
+ return true;
}
if (nr_unshown) {
pr_alert("BUG: Bad page map: %lu messages suppressed\n",
@@ -529,15 +515,91 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
}
if (nr_shown++ == 0)
resume = jiffies + 60 * HZ;
+ return false;
+}
+
+static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long addr)
+{
+ unsigned long long pgdv, p4dv, pudv, pmdv;
+ p4d_t p4d, *p4dp;
+ pud_t pud, *pudp;
+ pmd_t pmd, *pmdp;
+ pgd_t *pgdp;
+
+ /*
+ * Although this looks like a fully lockless pgtable walk, it is not:
+ * see locking requirements for print_bad_page_map().
+ */
+ pgdp = pgd_offset(mm, addr);
+ pgdv = pgd_val(*pgdp);
+
+ if (!pgd_present(*pgdp) || pgd_leaf(*pgdp)) {
+ pr_alert("pgd:%08llx\n", pgdv);
+ return;
+ }
+
+ p4dp = p4d_offset(pgdp, addr);
+ p4d = p4dp_get(p4dp);
+ p4dv = p4d_val(p4d);
+
+ if (!p4d_present(p4d) || p4d_leaf(p4d)) {
+ pr_alert("pgd:%08llx p4d:%08llx\n", pgdv, p4dv);
+ return;
+ }
+
+ pudp = pud_offset(p4dp, addr);
+ pud = pudp_get(pudp);
+ pudv = pud_val(pud);
+
+ if (!pud_present(pud) || pud_leaf(pud)) {
+ pr_alert("pgd:%08llx p4d:%08llx pud:%08llx\n", pgdv, p4dv, pudv);
+ return;
+ }
+
+ pmdp = pmd_offset(pudp, addr);
+ pmd = pmdp_get(pmdp);
+ pmdv = pmd_val(pmd);
+
+ /*
+ * Dumping the PTE would be nice, but it's tricky with CONFIG_HIGHPTE,
+ * because the table should already be mapped by the caller and
+ * doing another map would be bad. print_bad_page_map() should
+ * already take care of printing the PTE.
+ */
+ pr_alert("pgd:%08llx p4d:%08llx pud:%08llx pmd:%08llx\n", pgdv,
+ p4dv, pudv, pmdv);
+}
+
+/*
+ * This function is called to print an error when a bad page table entry (e.g.,
+ * corrupted page table entry) is found. For example, we might have a
+ * PFN-mapped pte in a region that doesn't allow it.
+ *
+ * The calling function must still handle the error.
+ *
+ * This function must be called during a proper page table walk, as it will
+ * re-walk the page table to dump information: the caller MUST prevent page
+ * table teardown (by holding mmap, vma or rmap lock) and MUST hold the leaf
+ * page table lock.
+ */
+static void print_bad_page_map(struct vm_area_struct *vma,
+ unsigned long addr, unsigned long long entry, struct page *page,
+ enum pgtable_level level)
+{
+ struct address_space *mapping;
+ pgoff_t index;
+
+ if (is_bad_page_map_ratelimited())
+ return;
mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
index = linear_page_index(vma, addr);
- pr_alert("BUG: Bad page map in process %s pte:%08llx pmd:%08llx\n",
- current->comm,
- (long long)pte_val(pte), (long long)pmd_val(*pmd));
+ pr_alert("BUG: Bad page map in process %s %s:%08llx", current->comm,
+ pgtable_level_to_str(level), entry);
+ __print_bad_page_map_pgtable(vma->vm_mm, addr);
if (page)
- dump_page(page, "bad pte");
+ dump_page(page, "bad page map");
pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n",
(void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
pr_alert("file:%pD fault:%ps mmap:%ps mmap_prepare: %ps read_folio:%ps\n",
@@ -549,6 +611,8 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
dump_stack();
add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
}
+#define print_bad_pte(vma, addr, pte, page) \
+ print_bad_page_map(vma, addr, pte_val(pte), page, PGTABLE_LEVEL_PTE)
/*
* vm_normal_page -- This function gets the "struct page" associated with a pte.
--
2.50.1On 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@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 <david@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 <david@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
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@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:
Out of interest do you know why this is happening? xtensa right? Does
xtensa not like CONFIG_DEBUG_VM?
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@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:
>
> 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
On Mon, Aug 11, 2025 at 01:26:28PM +0200, 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@redhat.com>
This LGTM, great explanations and thanks for the page table level stuff!
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.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";
> + }
> +}
> +
> #endif /* !__ASSEMBLY__ */
>
> #if !defined(MAX_POSSIBLE_PHYSMEM_BITS) && !defined(CONFIG_64BIT)
> diff --git a/mm/memory.c b/mm/memory.c
> index 626caedce35e0..dc0107354d37b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -491,22 +491,8 @@ static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
> add_mm_counter(mm, i, rss[i]);
> }
>
> -/*
> - * This function is called to print an error when a bad pte
> - * is found. For example, we might have a PFN-mapped pte in
> - * a region that doesn't allow it.
> - *
> - * The calling function must still handle the error.
> - */
> -static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
> - pte_t pte, struct page *page)
> +static bool is_bad_page_map_ratelimited(void)
> {
> - pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
> - p4d_t *p4d = p4d_offset(pgd, addr);
> - pud_t *pud = pud_offset(p4d, addr);
> - pmd_t *pmd = pmd_offset(pud, addr);
> - struct address_space *mapping;
> - pgoff_t index;
> static unsigned long resume;
> static unsigned long nr_shown;
> static unsigned long nr_unshown;
> @@ -518,7 +504,7 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
> if (nr_shown == 60) {
> if (time_before(jiffies, resume)) {
> nr_unshown++;
> - return;
> + return true;
> }
> if (nr_unshown) {
> pr_alert("BUG: Bad page map: %lu messages suppressed\n",
> @@ -529,15 +515,91 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
> }
> if (nr_shown++ == 0)
> resume = jiffies + 60 * HZ;
> + return false;
> +}
> +
> +static void __print_bad_page_map_pgtable(struct mm_struct *mm, unsigned long addr)
> +{
> + unsigned long long pgdv, p4dv, pudv, pmdv;
> + p4d_t p4d, *p4dp;
> + pud_t pud, *pudp;
> + pmd_t pmd, *pmdp;
> + pgd_t *pgdp;
> +
> + /*
> + * Although this looks like a fully lockless pgtable walk, it is not:
> + * see locking requirements for print_bad_page_map().
> + */
Thanks
> + pgdp = pgd_offset(mm, addr);
> + pgdv = pgd_val(*pgdp);
> +
> + if (!pgd_present(*pgdp) || pgd_leaf(*pgdp)) {
> + pr_alert("pgd:%08llx\n", pgdv);
> + return;
> + }
> +
> + p4dp = p4d_offset(pgdp, addr);
> + p4d = p4dp_get(p4dp);
> + p4dv = p4d_val(p4d);
> +
> + if (!p4d_present(p4d) || p4d_leaf(p4d)) {
> + pr_alert("pgd:%08llx p4d:%08llx\n", pgdv, p4dv);
> + return;
> + }
> +
> + pudp = pud_offset(p4dp, addr);
> + pud = pudp_get(pudp);
> + pudv = pud_val(pud);
> +
> + if (!pud_present(pud) || pud_leaf(pud)) {
> + pr_alert("pgd:%08llx p4d:%08llx pud:%08llx\n", pgdv, p4dv, pudv);
> + return;
> + }
> +
> + pmdp = pmd_offset(pudp, addr);
> + pmd = pmdp_get(pmdp);
> + pmdv = pmd_val(pmd);
> +
> + /*
> + * Dumping the PTE would be nice, but it's tricky with CONFIG_HIGHPTE,
Sigh, 32-bit.
> + * because the table should already be mapped by the caller and
> + * doing another map would be bad. print_bad_page_map() should
> + * already take care of printing the PTE.
> + */
> + pr_alert("pgd:%08llx p4d:%08llx pud:%08llx pmd:%08llx\n", pgdv,
> + p4dv, pudv, pmdv);
> +}
> +
> +/*
> + * This function is called to print an error when a bad page table entry (e.g.,
> + * corrupted page table entry) is found. For example, we might have a
> + * PFN-mapped pte in a region that doesn't allow it.
> + *
> + * The calling function must still handle the error.
> + *
> + * This function must be called during a proper page table walk, as it will
> + * re-walk the page table to dump information: the caller MUST prevent page
> + * table teardown (by holding mmap, vma or rmap lock) and MUST hold the leaf
> + * page table lock.
> + */
Thanks this is good!
> +static void print_bad_page_map(struct vm_area_struct *vma,
> + unsigned long addr, unsigned long long entry, struct page *page,
> + enum pgtable_level level)
> +{
> + struct address_space *mapping;
> + pgoff_t index;
> +
> + if (is_bad_page_map_ratelimited())
> + return;
>
> mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
> index = linear_page_index(vma, addr);
>
> - pr_alert("BUG: Bad page map in process %s pte:%08llx pmd:%08llx\n",
> - current->comm,
> - (long long)pte_val(pte), (long long)pmd_val(*pmd));
> + pr_alert("BUG: Bad page map in process %s %s:%08llx", current->comm,
> + pgtable_level_to_str(level), entry);
> + __print_bad_page_map_pgtable(vma->vm_mm, addr);
> if (page)
> - dump_page(page, "bad pte");
> + dump_page(page, "bad page map");
> pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n",
> (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
> pr_alert("file:%pD fault:%ps mmap:%ps mmap_prepare: %ps read_folio:%ps\n",
> @@ -549,6 +611,8 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
> dump_stack();
> add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> }
> +#define print_bad_pte(vma, addr, pte, page) \
> + print_bad_page_map(vma, addr, pte_val(pte), page, PGTABLE_LEVEL_PTE)
This is a nice abstraction.
>
> /*
> * vm_normal_page -- This function gets the "struct page" associated with a pte.
> --
> 2.50.1
>
© 2016 - 2025 Red Hat, Inc.