[RFC PATCH 1/7] mm: Add functions to track page directory modifications

Joerg Roedel
2020-05-08T14:40:57Z

From: Joerg Roedel <jroedel@suse.de>

Add page-table allocation functions which will keep track of changed
directory entries. They are needed for new PGD, P4D, PUD, and PMD
entries and will be used in vmalloc and ioremap code to decide whether
any changes in the kernel mappings need to be synchronized between
page-tables in the system.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
include/asm-generic/5level-fixup.h | 5 ++--
include/asm-generic/pgtable.h | 23 +++++++++++++++
include/linux/mm.h | 46 ++++++++++++++++++++++++++++++
3 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/5level-fixup.h b/include/asm-generic/5level-fixup.h
index 4c74b1c1d13b..58046ddc08d0 100644
--- a/include/asm-generic/5level-fixup.h
+++ b/include/asm-generic/5level-fixup.h
@@ -17,8 +17,9 @@
((unlikely(pgd_none(*(p4d))) && __pud_alloc(mm, p4d, address)) ? \
NULL : pud_offset(p4d, address))

-#define p4d_alloc(mm, pgd, address) (pgd)
-#define p4d_offset(pgd, start) (pgd)
+#define p4d_alloc(mm, pgd, address) (pgd)
+#define p4d_alloc_track(mm, pgd, address, mask) (pgd)
+#define p4d_offset(pgd, start) (pgd)

#ifndef __ASSEMBLY__
static inline int p4d_none(p4d_t p4d)
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 329b8c8ca703..bf1418ae91a2 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -1209,6 +1209,29 @@ static inline bool arch_has_pfn_modify_check(void)
# define PAGE_KERNEL_EXEC PAGE_KERNEL
#endif

+/*
+ * Page Table Modification bits for pgtbl_mod_mask.
+ *
+ * These are used by the p?d_alloc_track*() set of functions an in the generic
+ * vmalloc/ioremap code to track at which page-table levels entries have been
+ * modified. Based on that the code can better decide when vmalloc and ioremap
+ * mapping changes need to be synchronized to other page-tables in the system.
+ */
+#define __PGTBL_PGD_MODIFIED 0
+#define __PGTBL_P4D_MODIFIED 1
+#define __PGTBL_PUD_MODIFIED 2
+#define __PGTBL_PMD_MODIFIED 3
+#define __PGTBL_PTE_MODIFIED 4
+
+#define PGTBL_PGD_MODIFIED BIT(__PGTBL_PGD_MODIFIED)
+#define PGTBL_P4D_MODIFIED BIT(__PGTBL_P4D_MODIFIED)
+#define PGTBL_PUD_MODIFIED BIT(__PGTBL_PUD_MODIFIED)
+#define PGTBL_PMD_MODIFIED BIT(__PGTBL_PMD_MODIFIED)
+#define PGTBL_PTE_MODIFIED BIT(__PGTBL_PTE_MODIFIED)
+
+/* Page-Table Modification Mask */
+typedef unsigned int pgtbl_mod_mask;
+
#endif /* !__ASSEMBLY__ */

#ifndef io_remap_pfn_range
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5a323422d783..022fe682af9e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2078,13 +2078,54 @@ static inline pud_t *pud_alloc(struct mm_struct *mm, p4d_t *p4d,
return (unlikely(p4d_none(*p4d)) && __pud_alloc(mm, p4d, address)) ?
NULL : pud_offset(p4d, address);
}
+
+static inline p4d_t *p4d_alloc_track(struct mm_struct *mm, pgd_t *pgd,
+ unsigned long address,
+ pgtbl_mod_mask *mod_mask)
+
+{
+ if (unlikely(pgd_none(*pgd))) {
+ if (__p4d_alloc(mm, pgd, address))
+ return NULL;
+ *mod_mask |= PGTBL_PGD_MODIFIED;
+ }
+
+ return p4d_offset(pgd, address);
+}
+
#endif /* !__ARCH_HAS_5LEVEL_HACK */

+static inline pud_t *pud_alloc_track(struct mm_struct *mm, p4d_t *p4d,
+ unsigned long address,
+ pgtbl_mod_mask *mod_mask)
+{
+ if (unlikely(p4d_none(*p4d))) {
+ if (__pud_alloc(mm, p4d, address))
+ return NULL;
+ *mod_mask |= PGTBL_P4D_MODIFIED;
+ }
+
+ return pud_offset(p4d, address);
+}
+
static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
{
return (unlikely(pud_none(*pud)) && __pmd_alloc(mm, pud, address))?
NULL: pmd_offset(pud, address);
}
+
+static inline pmd_t *pmd_alloc_track(struct mm_struct *mm, pud_t *pud,
+ unsigned long address,
+ pgtbl_mod_mask *mod_mask)
+{
+ if (unlikely(pud_none(*pud))) {
+ if (__pmd_alloc(mm, pud, address))
+ return NULL;
+ *mod_mask |= PGTBL_PUD_MODIFIED;
+ }
+
+ return pmd_offset(pud, address);
+}
#endif /* CONFIG_MMU */

#if USE_SPLIT_PTE_PTLOCKS
@@ -2200,6 +2241,11 @@ static inline void pgtable_pte_page_dtor(struct page *page)
((unlikely(pmd_none(*(pmd))) && __pte_alloc_kernel(pmd))? \
NULL: pte_offset_kernel(pmd, address))

+#define pte_alloc_kernel_track(pmd, address, mask) \
+ ((unlikely(pmd_none(*(pmd))) && \
+ (__pte_alloc_kernel(pmd) || ({*(mask)|=PGTBL_PMD_MODIFIED;0;})))?\
+ NULL: pte_offset_kernel(pmd, address))
+
#if USE_SPLIT_PMD_PTLOCKS

static struct page *pmd_to_page(pmd_t *pmd)
--
2.17.1