[PATCH v3 3/3] powerpc/mm/cxl: Add the fault handling cpu to mm cpumask

[Aneesh Kumar K.V]

We use mm cpumask for serializing against lockless page table walk. Anybody
who is doing a lockless page table walk is expected to disable irq and only
cpus in mm cpumask is expected do the lockless walk. This ensure that
a THP split can send IPI to only cpus in the mm cpumask, to make sure there
are no parallel lockless page table walk.

Add the CAPI fault handling cpu to the mm cpumask so that we can do the lockless
page table walk while inserting hash page table entries.

Reviewed-by: Frederic Barrat <fbarrat at linux.vnet.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
---
 arch/powerpc/mm/pgtable-book3s64.c | 10 +---------
 drivers/misc/cxl/fault.c           |  6 ++++++
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
index 57b947cde2bf..3b65917785a5 100644
--- a/arch/powerpc/mm/pgtable-book3s64.c
+++ b/arch/powerpc/mm/pgtable-book3s64.c
@@ -83,15 +83,7 @@ static void do_nothing(void *unused)
 void serialize_against_pte_lookup(struct mm_struct *mm)
 {
 	smp_mb();
-	/*
-	 * Cxl fault handling requires us to do a lockless page table
-	 * walk while inserting hash page table entry with mm tracked
-	 * in cxl context. Hence we need to do a global flush.
-	 */
-	if (cxl_ctx_in_use())
-		smp_call_function(do_nothing, NULL, 1);
-	else
-		smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1);
+	smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1);
 }
 
 /*
diff --git a/drivers/misc/cxl/fault.c b/drivers/misc/cxl/fault.c
index 6eed7d03e2b5..ab507e4ed69b 100644
--- a/drivers/misc/cxl/fault.c
+++ b/drivers/misc/cxl/fault.c
@@ -138,6 +138,12 @@ int cxl_handle_mm_fault(struct mm_struct *mm, u64 dsisr, u64 dar)
 	int result;
 	unsigned long access, flags, inv_flags = 0;
 
+	/*
+	 * 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.
+	 */
+	cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
 	if ((result = copro_handle_mm_fault(mm, dar, dsisr, &flt))) {
 		pr_devel("copro_handle_mm_fault failed: %#x\n", result);
 		return result;
-- 
2.13.3