On 28.04.25 18:08, Peter Xu wrote:
On Fri, Apr 25, 2025 at 10:36:55PM +0200, David Hildenbrand wrote:
On 25.04.25 22:23, Peter Xu wrote:
On Fri, Apr 25, 2025 at 10:17:09AM +0200, David Hildenbrand wrote:
Let's use our new interface. In remap_pfn_range(), we'll now decide
whether we have to track (full VMA covered) or only sanitize the pgprot
(partial VMA covered).
Remember what we have to untrack by linking it from the VMA. When
duplicating VMAs (e.g., splitting, mremap, fork), we'll handle it similar
to anon VMA names, and use a kref to share the tracking.
Once the last VMA un-refs our tracking data, we'll do the untracking,
which simplifies things a lot and should sort our various issues we saw
recently, for example, when partially unmapping/zapping a tracked VMA.
This change implies that we'll keep tracking the original PFN range even
after splitting + partially unmapping it: not too bad, because it was
not working reliably before. The only thing that kind-of worked before
was shrinking such a mapping using mremap(): we managed to adjust the
reservation in a hacky way, now we won't adjust the reservation but
leave it around until all involved VMAs are gone.
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
include/linux/mm_inline.h | 2 +
include/linux/mm_types.h | 11 ++++++
kernel/fork.c | 54 ++++++++++++++++++++++++--
mm/memory.c | 81 +++++++++++++++++++++++++++++++--------
mm/mremap.c | 4 --
5 files changed, 128 insertions(+), 24 deletions(-)
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index f9157a0c42a5c..89b518ff097e6 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -447,6 +447,8 @@ static inline bool anon_vma_name_eq(struct anon_vma_name
*anon_name1,
#endif /* CONFIG_ANON_VMA_NAME */
+void pfnmap_track_ctx_release(struct kref *ref);
+
static inline void init_tlb_flush_pending(struct mm_struct *mm)
{
atomic_set(&mm->tlb_flush_pending, 0);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 56d07edd01f91..91124761cfda8 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -764,6 +764,14 @@ struct vma_numab_state {
int prev_scan_seq;
};
+#ifdef __HAVE_PFNMAP_TRACKING
+struct pfnmap_track_ctx {
+ struct kref kref;
+ unsigned long pfn;
+ unsigned long size;
+};
+#endif
+
/*
* This struct describes a virtual memory area. There is one of these
* per VM-area/task. A VM area is any part of the process virtual memory
@@ -877,6 +885,9 @@ struct vm_area_struct {
struct anon_vma_name *anon_name;
#endif
struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
+#ifdef __HAVE_PFNMAP_TRACKING
+ struct pfnmap_track_ctx *pfnmap_track_ctx;
+#endif
So this was originally the small concern (or is it small?) that this will
grow every vma on x86, am I right?
Yeah, and last time I looked into this, it would have grown it such that it
would
require a bigger slab. Right now:
Probably due to what config you have. E.g., when I'm looking mine it's
much bigger and already consuming 256B, but it's because I enabled more
things (userfaultfd, lockdep, etc.).
Note that I enabled everything that you would expect on a production
system (incld. userfaultfd, mempolicy, per-vma locks), so I didn't
enable lockep.
Thanks for verifying!
--
Cheers,
David / dhildenb
