On Fri, Aug 21, 2020 at 10:54:22AM +0100, Chris Wilson wrote: > Ok. I thought it had to be after assigning the *ptep. If we apply the > sync first, do not have to worry about PGTBL_PTE_MODIFIED from the > *ptep? Hmm, if I understand the code correctly, you are re-implementing some generic ioremap/vmalloc mapping logic in the i915 driver. I don't know the reason, but if it is valid you need to manually call arch_sync_kernel_mappings() from your driver like this to be correct: if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PTE_MODIFIED) arch_sync_kernel_mappings(); In practice this is a no-op, because nobody sets PGTBL_PTE_MODIFIED in ARCH_PAGE_TABLE_SYNC_MASK, so the above code would be optimized away. But what you really care about is the tracking in apply_to_page_range(), as that allocates the !pte levels of your page-table, which needs synchronization on x86-32. Btw, what are the reasons you can't use generic vmalloc/ioremap interfaces to map the range? Regards, Joerg
