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a=a-qgeE7W1pNrGK8U0ZQC:22 a=uAr15Ul7AJ1q7o2wzYQp:22 a=kIIFJ0VLUOy1gFZzwZHL:22 a=WzC6qhA0u3u7Ye7llzcV:22 a=1CNFftbPRP8L7MoqJWF3:22 a=HkZW87K1Qel5hWWM3VKY:22 X-Proofpoint-ORIG-GUID: Zco3XGbg1y_DT4WDZ1nHPKWw9T8yB2qC 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: > > > > > > 1) 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. > > > > > > 2) 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 > > > Acked-by: Kiryl Shutsemau > > > Reviewed-by: Mike Rapoport (Microsoft) > > > Reviewed-by: Lorenzo Stoakes > > > Acked-by: David Hildenbrand > > > Cc: Alexander Potapenko > > > Cc: Alistair Popple > > > Cc: Andrey Konovalov > > > Cc: Andrey Ryabinin > > > Cc: Andy Lutomirski > > > Cc: Aneesh Kumar K.V > > > Cc: Anshuman Khandual > > > Cc: Ard Biesheuvel > > > Cc: Arnd Bergmann > > > Cc: bibo mao > > > Cc: Borislav Betkov > > > Cc: Christoph Lameter (Ampere) > > > Cc: Dennis Zhou > > > Cc: Dev Jain > > > Cc: Dmitriy Vyukov > > > Cc: Gwan-gyeong Mun > > > Cc: Ingo Molnar > > > Cc: Jane Chu > > > Cc: Joao Martins > > > Cc: Joerg Roedel > > > Cc: John Hubbard > > > Cc: Kevin Brodsky > > > Cc: Liam Howlett > > > Cc: Michal Hocko > > > Cc: Oscar Salvador > > > Cc: Peter Xu > > > Cc: Peter Zijlstra > > > Cc: Qi Zheng > > > Cc: Ryan Roberts > > > Cc: Suren Baghdasaryan > > > Cc: Tejun Heo > > > Cc: Thomas Gleinxer > > > Cc: Thomas Huth > > > Cc: Uladzislau Rezki (Sony) > > > Cc: Vincenzo Frascino > > > Cc: Vlastimil Babka > > > Cc: Pedro Falcato > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Andrew Morton > > > [ Adjust context ] > > > Signed-off-by: Harry Yoo > > > --- > > > 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! -- Cheers, Harry / Hyeonggon