[PATCH 1/4] mm: Export flush_vm_area() to sync the PTEs upon construction

[Chris Wilson]

The alloc_vm_area() is another method for drivers to
vmap/map_kernel_range that uses apply_to_page_range() rather than the
direct vmalloc walkers. This is missing the page table modification
tracking, and the ability to synchronize the PTE updates afterwards.
Provide flush_vm_area() for the users of alloc_vm_area() that assumes
the worst and ensures that the page directories are correctly flushed
upon construction.

The impact is most pronounced on x86_32 due to the delayed set_pmd().

Reported-by: Pavel Machek <pavel@xxxxxx>
References: 2ba3e6947aed ("mm/vmalloc: track which page-table levels were modified")
References: 86cf69f1d893 ("x86/mm/32: implement arch_sync_kernel_mappings()")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.8+
---
 include/linux/vmalloc.h |  1 +
 mm/vmalloc.c            | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 0221f852a7e1..a253b27df0ac 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -204,6 +204,7 @@ static inline void set_vm_flush_reset_perms(void *addr)
 
 /* Allocate/destroy a 'vmalloc' VM area. */
 extern struct vm_struct *alloc_vm_area(size_t size, pte_t **ptes);
+extern void flush_vm_area(struct vm_struct *area);
 extern void free_vm_area(struct vm_struct *area);
 
 /* for /dev/kmem */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index b482d240f9a2..c41934486031 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3078,6 +3078,22 @@ struct vm_struct *alloc_vm_area(size_t size, pte_t **ptes)
 }
 EXPORT_SYMBOL_GPL(alloc_vm_area);
 
+void flush_vm_area(struct vm_struct *area)
+{
+	unsigned long addr = (unsigned long)area->addr;
+
+	/* apply_to_page_range() doesn't track the damage, assume the worst */
+	if (ARCH_PAGE_TABLE_SYNC_MASK & (PGTBL_PTE_MODIFIED |
+					 PGTBL_PMD_MODIFIED |
+					 PGTBL_PUD_MODIFIED |
+					 PGTBL_P4D_MODIFIED |
+					 PGTBL_PGD_MODIFIED))
+		arch_sync_kernel_mappings(addr, addr + area->size);
+
+	flush_cache_vmap(addr, area->size);
+}
+EXPORT_SYMBOL_GPL(flush_vm_area);
+
 void free_vm_area(struct vm_struct *area)
 {
 	struct vm_struct *ret;
-- 
2.20.1