On 28/08/17 18:35, Aneesh Kumar K.V wrote:
We need to add memory barrier so that the page table walk doesn't happen
before the cpumask is set and made visible to the other cpus. We need
to use a sync here instead of lwsync because lwsync is not sufficient for
store/load ordering.
We also need to add an if (mm) check so that we do the right thing when called
with a kernel context. For kernel context, we have mm = NULL. W.r.t kernel
address we can skip setting the mm cpumask.
Fixes: 0f4bc0932e ("powerpc/mm/cxl: Add the fault handling cpu to mm cpumask")
Cc: Andrew Donnellan <andrew.donnel...@au1.ibm.com>
Reported-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Reported-by: Dan Carpenter <dan.carpen...@oracle.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
Acked-by: Andrew Donnellan <andrew.donnel...@au1.ibm.com>
---
drivers/misc/cxl/fault.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/misc/cxl/fault.c b/drivers/misc/cxl/fault.c
index ab507e4ed69b..f17f72ea0545 100644
--- a/drivers/misc/cxl/fault.c
+++ b/drivers/misc/cxl/fault.c
@@ -141,9 +141,19 @@ int cxl_handle_mm_fault(struct mm_struct *mm, u64 dsisr,
u64 dar)
/*
* Add the fault handling cpu to task mm cpumask so that we
* can do a safe lockless page table walk when inserting the
- * hash page table entry.
+ * hash page table entry. This function get called with a
+ * valid mm for user space addresses. Hence using the if (mm)
+ * check is sufficient here.
*/
- cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
+ if (mm && !cpumask_test_cpu(smp_processor_id(), mm_cpumask(mm))) {
+ cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
+ /*
+ * We need to make sure we walk the table only after
+ * we update the cpumask. The other side of the barrier
+ * is explained in serialize_against_pte_lookup()
+ */
+ smp_mb();
+ }
if ((result = copro_handle_mm_fault(mm, dar, dsisr, &flt))) {
pr_devel("copro_handle_mm_fault failed: %#x\n", result);
return result;
--
Andrew Donnellan OzLabs, ADL Canberra
andrew.donnel...@au1.ibm.com IBM Australia Limited
