[PATCH v4 04/11] kernel/fork: Initialize mm's PASID

Fenghua Yu
2022-02-08T01:05:01Z

A new mm doesn't have a PASID yet when it's created. Initialize
the mm's PASID on fork() or for init_mm to INVALID_IOASID (-1).

INIT_PASID (0) is reserved for kernel legacy DMA PASID. It cannot be
allocated to a user process. Initializing the process's PASID to 0 may
cause confusion that why the process uses the reserved kernel legacy DMA
PASID. Initializing the PASID to INVALID_IOASID (-1) explicitly
tells the process doesn't have a valid PASID yet.

Even though the only user of mm_pasid_init() is in fork.c, define it
in <linux/sched/mm.h> as the first of three mm/pasid life cycle
functions (init/set/drop) to keep these all together.

Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
v4:
- Update the commit message to explain why init pasid to -1 and why
define mm_pasid_init() (Thomas)

v2:
- Change condition to more accurate CONFIG_IOMMU_SVA (Jacob)

include/linux/sched/mm.h | 10 ++++++++++
kernel/fork.c | 10 ++--------
mm/init-mm.c | 4 ++++
3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index aa5f09ca5bcf..c74d1edbac2f 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -8,6 +8,7 @@
#include <linux/mm_types.h>
#include <linux/gfp.h>
#include <linux/sync_core.h>
+#include <linux/ioasid.h>

/*
* Routines for handling mm_structs
@@ -433,4 +434,13 @@ static inline void membarrier_update_current_mm(struct mm_struct *next_mm)
}
#endif

+#ifdef CONFIG_IOMMU_SVA
+static inline void mm_pasid_init(struct mm_struct *mm)
+{
+ mm->pasid = INVALID_IOASID;
+}
+#else
+static inline void mm_pasid_init(struct mm_struct *mm) {}
+#endif
+
#endif /* _LINUX_SCHED_MM_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 6ee7551d3bd2..deacd2c17a7f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -97,6 +97,7 @@
#include <linux/scs.h>
#include <linux/io_uring.h>
#include <linux/bpf.h>
+#include <linux/sched/mm.h>

#include <asm/pgalloc.h>
#include <linux/uaccess.h>
@@ -1019,13 +1020,6 @@ static void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
#endif
}

-static void mm_init_pasid(struct mm_struct *mm)
-{
-#ifdef CONFIG_IOMMU_SVA
- mm->pasid = INIT_PASID;
-#endif
-}
-
static void mm_init_uprobes_state(struct mm_struct *mm)
{
#ifdef CONFIG_UPROBES
@@ -1054,7 +1048,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
mm_init_cpumask(mm);
mm_init_aio(mm);
mm_init_owner(mm, p);
- mm_init_pasid(mm);
+ mm_pasid_init(mm);
RCU_INIT_POINTER(mm->exe_file, NULL);
mmu_notifier_subscriptions_init(mm);
init_tlb_flush_pending(mm);
diff --git a/mm/init-mm.c b/mm/init-mm.c
index b4a6f38fb51d..fbe7844d0912 100644
--- a/mm/init-mm.c
+++ b/mm/init-mm.c
@@ -10,6 +10,7 @@

#include <linux/atomic.h>
#include <linux/user_namespace.h>
+#include <linux/ioasid.h>
#include <asm/mmu.h>

#ifndef INIT_MM_CONTEXT
@@ -38,6 +39,9 @@ struct mm_struct init_mm = {
.mmlist = LIST_HEAD_INIT(init_mm.mmlist),
.user_ns = &init_user_ns,
.cpu_bitmap = CPU_BITS_NONE,
+#ifdef CONFIG_IOMMU_SVA
+ .pasid = INVALID_IOASID,
+#endif
INIT_MM_CONTEXT(init_mm)
};

--
2.35.1