On Fri, Aug 21, 2020 at 09:50:08AM +0100, Chris Wilson wrote:
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@ucw.cz 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@chris-wilson.co.uk Cc: Andrew Morton akpm@linux-foundation.org Cc: Joerg Roedel jroedel@suse.de Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Dave Airlie airlied@redhat.com Cc: Joonas Lahtinen joonas.lahtinen@linux.intel.com Cc: Rodrigo Vivi rodrigo.vivi@intel.com Cc: Pavel Machek pavel@ucw.cz Cc: David Vrabel david.vrabel@citrix.com Cc: stable@vger.kernel.org # 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);
This should happen in __apply_to_page_range() directly and look like this:
if (ARCH_PAGE_TABLE_SYNC_MASK && create) arch_sync_kernel_mappings(addr, addr + size);
Or even better, track whether something had to be allocated in the __apply_to_page_range() path and check for:
if (ARCH_PAGE_TABLE_SYNC_MASK & mask)