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Diffstat (limited to 'Documentation/mm/page_table_check.rst')
| -rw-r--r-- | Documentation/mm/page_table_check.rst | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/Documentation/mm/page_table_check.rst b/Documentation/mm/page_table_check.rst index cfd8f4117cf3..c12838ce6b8d 100644 --- a/Documentation/mm/page_table_check.rst +++ b/Documentation/mm/page_table_check.rst @@ -52,3 +52,22 @@ Build kernel with: Optionally, build kernel with PAGE_TABLE_CHECK_ENFORCED in order to have page table support without extra kernel parameter. + +Implementation notes +==================== + +We specifically decided not to use VMA information in order to avoid relying on +MM states (except for limited "struct page" info). The page table check is a +separate from Linux-MM state machine that verifies that the user accessible +pages are not falsely shared. + +PAGE_TABLE_CHECK depends on EXCLUSIVE_SYSTEM_RAM. The reason is that without +EXCLUSIVE_SYSTEM_RAM, users are allowed to map arbitrary physical memory +regions into the userspace via /dev/mem. At the same time, pages may change +their properties (e.g., from anonymous pages to named pages) while they are +still being mapped in the userspace, leading to "corruption" detected by the +page table check. + +Even with EXCLUSIVE_SYSTEM_RAM, I/O pages may be still allowed to be mapped via +/dev/mem. However, these pages are always considered as named pages, so they +won't break the logic used in the page table check. |