Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
Documentation/vm/mmu_notifier.txt | 108 ++++++++++++++++++++------------------
1 file changed, 57 insertions(+), 51 deletions(-)
diff --git a/Documentation/vm/mmu_notifier.txt b/Documentation/vm/mmu_notifier.txt
index 23b4625..47baa1c 100644
--- a/Documentation/vm/mmu_notifier.txt
+++ b/Documentation/vm/mmu_notifier.txt
@@ -1,7 +1,10 @@
+.. _mmu_notifier:
+
When do you need to notify inside page table lock ?
+===================================================
When clearing a pte/pmd we are given a choice to notify the event through
-(notify version of *_clear_flush call mmu_notifier_invalidate_range) under
+(notify version of \*_clear_flush call mmu_notifier_invalidate_range) under
the page table lock. But that notification is not necessary in all cases.
For secondary TLB (non CPU TLB) like IOMMU TLB or device TLB (when device use
@@ -18,6 +21,7 @@ a page that might now be used by some completely different task.
Case B is more subtle. For correctness it requires the following sequence to
happen:
+
- take page table lock
- clear page table entry and notify ([pmd/pte]p_huge_clear_flush_notify())
- set page table entry to point to new page
@@ -28,58 +32,60 @@ the device.
Consider the following scenario (device use a feature similar to ATS/PASID):
-Two address addrA and addrB such that |addrA - addrB| >= PAGE_SIZE we assume
+Two address addrA and addrB such that \|addrA - addrB\| >= PAGE_SIZE we assume
they are write protected for COW (other case of B apply too).
-[Time N] --------------------------------------------------------------------
-CPU-thread-0 {try to write to addrA}
-CPU-thread-1 {try to write to addrB}
-CPU-thread-2 {}
-CPU-thread-3 {}
-DEV-thread-0 {read addrA and populate device TLB}
-DEV-thread-2 {read addrB and populate device TLB}
-[Time N+1] ------------------------------------------------------------------
-CPU-thread-0 {COW_step0: {mmu_notifier_invalidate_range_start(addrA)}}
-CPU-thread-1 {COW_step0: {mmu_notifier_invalidate_range_start(addrB)}}
-CPU-thread-2 {}
-CPU-thread-3 {}
-DEV-thread-0 {}
-DEV-thread-2 {}
-[Time N+2] ------------------------------------------------------------------
-CPU-thread-0 {COW_step1: {update page table to point to new page for addrA}}
-CPU-thread-1 {COW_step1: {update page table to point to new page for addrB}}
-CPU-thread-2 {}
-CPU-thread-3 {}
-DEV-thread-0 {}
-DEV-thread-2 {}
-[Time N+3] ------------------------------------------------------------------
-CPU-thread-0 {preempted}
-CPU-thread-1 {preempted}
-CPU-thread-2 {write to addrA which is a write to new page}
-CPU-thread-3 {}
-DEV-thread-0 {}
-DEV-thread-2 {}
-[Time N+3] ------------------------------------------------------------------
-CPU-thread-0 {preempted}
-CPU-thread-1 {preempted}
-CPU-thread-2 {}
-CPU-thread-3 {write to addrB which is a write to new page}
-DEV-thread-0 {}
-DEV-thread-2 {}
-[Time N+4] ------------------------------------------------------------------
-CPU-thread-0 {preempted}
-CPU-thread-1 {COW_step3: {mmu_notifier_invalidate_range_end(addrB)}}
-CPU-thread-2 {}
-CPU-thread-3 {}
-DEV-thread-0 {}
-DEV-thread-2 {}
-[Time N+5] ------------------------------------------------------------------
-CPU-thread-0 {preempted}
-CPU-thread-1 {}
-CPU-thread-2 {}
-CPU-thread-3 {}
-DEV-thread-0 {read addrA from old page}
-DEV-thread-2 {read addrB from new page}
+::
+
+ [Time N] --------------------------------------------------------------------
+ CPU-thread-0 {try to write to addrA}
+ CPU-thread-1 {try to write to addrB}
+ CPU-thread-2 {}
+ CPU-thread-3 {}
+ DEV-thread-0 {read addrA and populate device TLB}
+ DEV-thread-2 {read addrB and populate device TLB}
+ [Time N+1] ------------------------------------------------------------------
+ CPU-thread-0 {COW_step0: {mmu_notifier_invalidate_range_start(addrA)}}
+ CPU-thread-1 {COW_step0: {mmu_notifier_invalidate_range_start(addrB)}}
+ CPU-thread-2 {}
+ CPU-thread-3 {}
+ DEV-thread-0 {}
+ DEV-thread-2 {}
+ [Time N+2] ------------------------------------------------------------------
+ CPU-thread-0 {COW_step1: {update page table to point to new page for addrA}}
+ CPU-thread-1 {COW_step1: {update page table to point to new page for addrB}}
+ CPU-thread-2 {}
+ CPU-thread-3 {}
+ DEV-thread-0 {}
+ DEV-thread-2 {}
+ [Time N+3] ------------------------------------------------------------------
+ CPU-thread-0 {preempted}
+ CPU-thread-1 {preempted}
+ CPU-thread-2 {write to addrA which is a write to new page}
+ CPU-thread-3 {}
+ DEV-thread-0 {}
+ DEV-thread-2 {}
+ [Time N+3] ------------------------------------------------------------------
+ CPU-thread-0 {preempted}
+ CPU-thread-1 {preempted}
+ CPU-thread-2 {}
+ CPU-thread-3 {write to addrB which is a write to new page}
+ DEV-thread-0 {}
+ DEV-thread-2 {}
+ [Time N+4] ------------------------------------------------------------------
+ CPU-thread-0 {preempted}
+ CPU-thread-1 {COW_step3: {mmu_notifier_invalidate_range_end(addrB)}}
+ CPU-thread-2 {}
+ CPU-thread-3 {}
+ DEV-thread-0 {}
+ DEV-thread-2 {}
+ [Time N+5] ------------------------------------------------------------------
+ CPU-thread-0 {preempted}
+ CPU-thread-1 {}
+ CPU-thread-2 {}
+ CPU-thread-3 {}
+ DEV-thread-0 {read addrA from old page}
+ DEV-thread-2 {read addrB from new page}
So here because at time N+2 the clear page table entry was not pair with a
notification to invalidate the secondary TLB, the device see the new value for
--
2.7.4
