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Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 11, 2025 at 07:46:13AM +0100, Kiryl Shutsemau wrote: > On Mon, Aug 11, 2025 at 02:34:17PM +0900, Harry Yoo wrote: > > # The solution: Make page table sync more code robust and harder to miss > > > > To address this, Dave Hansen suggested [3] [4] introducing > > {pgd,p4d}_populate_kernel() for updating kernel portion > > of the page tables and allow each architecture to explicitly perform > > synchronization when installing top-level entries. With this approach, > > we no longer need to worry about missing the sync step, reducing the risk > > of future regressions. > > Looks sane: > > Acked-by: Kiryl Shutsemau Thanks a lot, Kiryl! > > The new interface reuses existing ARCH_PAGE_TABLE_SYNC_MASK, > > PGTBL_P*D_MODIFIED and arch_sync_kernel_mappings() facility used by > > vmalloc and ioremap to synchronize page tables. > > > > pgd_populate_kernel() looks like this: > > static inline void pgd_populate_kernel(unsigned long addr, pgd_t *pgd, > > p4d_t *p4d) > > { > > pgd_populate(&init_mm, pgd, p4d); > > if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED) > > arch_sync_kernel_mappings(addr, addr); > > } > > > > It is worth noting that vmalloc() and apply_to_range() carefully > > synchronizes page tables by calling p*d_alloc_track() and > > arch_sync_kernel_mappings(), and thus they are not affected by > > this patch series. > Well, except ARCH_PAGE_TABLE_SYNC_MASK is not defined on x86-64 until > now. So I think it is affected. Oh, you are right. Although they don't use p*d_populate_kernel() API, changing ARCH_PAGE_TABLE_SYNC_MASK affects their behavior. PGD entries for vmalloc are always pre-populated so it shouldn't be affected much. But apply_to_page_range() is. Though I'm not aware of any bugs from it spanning multiple PGD ranges and missing page table sync. By the way, I think it may be better in the future to unify them under the same logic for synchronizing kernel mappings. With this series, there are two ways: 1. p*d_populate_kernel() 2. p*d_alloc_track() + arch_sync_kernel_mappings. -- Cheers, Harry / Hyeonggon > -- > Kiryl Shutsemau / Kirill A. Shutemov