On Tue, Sep 09, 2025 at 03:52:35PM +0200, Greg KH wrote:
On Tue, Sep 09, 2025 at 03:52:14PM +0200, Greg KH wrote:
On Tue, Sep 09, 2025 at 02:54:32PM +0900, Harry Yoo wrote:
Introduce and use {pgd,p4d}_populate_kernel() in core MM code when populating PGD and P4D entries for the kernel address space. These helpers ensure proper synchronization of page tables when updating the kernel portion of top-level page tables.
Until now, the kernel has relied on each architecture to handle synchronization of top-level page tables in an ad-hoc manner. For example, see commit 9b861528a801 ("x86-64, mem: Update all PGDs for direct mapping and vmemmap mapping changes").
However, this approach has proven fragile for following reasons:
It is easy to forget to perform the necessary page table synchronization when introducing new changes. For instance, commit 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory savings for compound devmaps") overlooked the need to synchronize page tables for the vmemmap area.
It is also easy to overlook that the vmemmap and direct mapping areas must not be accessed before explicit page table synchronization. For example, commit 8d400913c231 ("x86/vmemmap: handle unpopulated sub-pmd ranges")) caused crashes by accessing the vmemmap area before calling sync_global_pgds().
To address this, as suggested by Dave Hansen, introduce _kernel() variants of the page table population helpers, which invoke architecture-specific hooks to properly synchronize page tables. These are introduced in a new header file, include/linux/pgalloc.h, so they can be called from common code.
They reuse existing infrastructure for vmalloc and ioremap. Synchronization requirements are determined by ARCH_PAGE_TABLE_SYNC_MASK, and the actual synchronization is performed by arch_sync_kernel_mappings().
This change currently targets only x86_64, so only PGD and P4D level helpers are introduced. Currently, these helpers are no-ops since no architecture sets PGTBL_{PGD,P4D}_MODIFIED in ARCH_PAGE_TABLE_SYNC_MASK.
In theory, PUD and PMD level helpers can be added later if needed by other architectures. For now, 32-bit architectures (x86-32 and arm) only handle PGTBL_PMD_MODIFIED, so p*d_populate_kernel() will never affect them unless we introduce a PMD level helper.
[harry.yoo@oracle.com: fix KASAN build error due to p*d_populate_kernel()] Link: https://lkml.kernel.org/r/20250822020727.202749-1-harry.yoo@oracle.com Link: https://lkml.kernel.org/r/20250818020206.4517-3-harry.yoo@oracle.com Fixes: 8d400913c231 ("x86/vmemmap: handle unpopulated sub-pmd ranges") Suggested-by: Dave Hansen dave.hansen@linux.intel.com Acked-by: Kiryl Shutsemau kas@kernel.org Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Acked-by: David Hildenbrand david@redhat.com Cc: Alexander Potapenko glider@google.com Cc: Alistair Popple apopple@nvidia.com Cc: Andrey Konovalov andreyknvl@gmail.com Cc: Andrey Ryabinin ryabinin.a.a@gmail.com Cc: Andy Lutomirski luto@kernel.org Cc: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Ard Biesheuvel ardb@kernel.org Cc: Arnd Bergmann arnd@arndb.de Cc: bibo mao maobibo@loongson.cn Cc: Borislav Betkov bp@alien8.de Cc: Christoph Lameter (Ampere) cl@gentwo.org Cc: Dennis Zhou dennis@kernel.org Cc: Dev Jain dev.jain@arm.com Cc: Dmitriy Vyukov dvyukov@google.com Cc: Gwan-gyeong Mun gwan-gyeong.mun@intel.com Cc: Ingo Molnar mingo@redhat.com Cc: Jane Chu jane.chu@oracle.com Cc: Joao Martins joao.m.martins@oracle.com Cc: Joerg Roedel joro@8bytes.org Cc: John Hubbard jhubbard@nvidia.com Cc: Kevin Brodsky kevin.brodsky@arm.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Michal Hocko mhocko@suse.com Cc: Oscar Salvador osalvador@suse.de Cc: Peter Xu peterx@redhat.com Cc: Peter Zijlstra peterz@infradead.org Cc: Qi Zheng zhengqi.arch@bytedance.com Cc: Ryan Roberts ryan.roberts@arm.com Cc: Suren Baghdasaryan surenb@google.com Cc: Tejun Heo tj@kernel.org Cc: Thomas Gleinxer tglx@linutronix.de Cc: Thomas Huth thuth@redhat.com Cc: Uladzislau Rezki (Sony) urezki@gmail.com Cc: Vincenzo Frascino vincenzo.frascino@arm.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Pedro Falcato pfalcato@suse.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org [ Adjust context ] Signed-off-by: Harry Yoo harry.yoo@oracle.com
include/linux/pgalloc.h | 29 +++++++++++++++++++++++++++++ include/linux/pgtable.h | 13 +++++++------ mm/kasan/init.c | 12 ++++++------ mm/percpu.c | 6 +++--- mm/sparse-vmemmap.c | 6 +++--- 5 files changed, 48 insertions(+), 18 deletions(-) create mode 100644 include/linux/pgalloc.h
Can you resend these with the upstream git id from Linus's tree in it, so we know how to compare it with the original?
Same for the other backports, sorry I forgot to say that here.
It's
commit f2d2f9598ebb0158a3fe17cda0106d7752e654a2 upstream.
Sorry for the inconvenience, I'll resend it with the upstream git id.
Thanks!