Add a late PGD init callback to places that allocate a new MM
with a new PGD: copy_process() and exec().
The purpose of this callback is to allow architectures to implement
lockless initialization of task PGDs, to remove the scalability
limit of pgd_list/pgd_lock.
Architectures can opt in to this callback via the ARCH_HAS_PGD_INIT_LATE
Kconfig flag. There's zero overhead on architectures that are not using it.
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Waiman Long <Waiman.Long@xxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/Kconfig | 9 +++++++++
fs/exec.c | 3 +++
include/linux/mm.h | 6 ++++++
kernel/fork.c | 16 ++++++++++++++++
4 files changed, 34 insertions(+)
diff --git a/arch/Kconfig b/arch/Kconfig
index a65eafb24997..a8e866cd4247 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -491,6 +491,15 @@ config PGTABLE_LEVELS
int
default 2
+config ARCH_HAS_PGD_INIT_LATE
+ bool
+ help
+ Architectures that want a late PGD initialization can define
+ the arch_pgd_init_late() callback and it will be called
+ by the generic new task (fork()) code after a new task has
+ been made visible on the task list, but before it has been
+ first scheduled.
+
config ARCH_HAS_ELF_RANDOMIZE
bool
help
diff --git a/fs/exec.c b/fs/exec.c
index 1977c2a553ac..4ce1383d5bba 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -860,7 +860,10 @@ static int exec_mmap(struct mm_struct *mm)
}
task_lock(tsk);
active_mm = tsk->active_mm;
+
tsk->mm = mm;
+ arch_pgd_init_late(mm);
+
tsk->active_mm = mm;
activate_mm(active_mm, mm);
tsk->mm->vmacache_seqnum = 0;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0755b9fd03a7..a3edc839e431 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1134,6 +1134,12 @@ int follow_phys(struct vm_area_struct *vma, unsigned long address,
int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
void *buf, int len, int write);
+#ifdef CONFIG_ARCH_HAS_PGD_INIT_LATE
+void arch_pgd_init_late(struct mm_struct *mm);
+#else
+static inline void arch_pgd_init_late(struct mm_struct *mm) { }
+#endif
+
static inline void unmap_shared_mapping_range(struct address_space *mapping,
loff_t const holebegin, loff_t const holelen)
{
diff --git a/kernel/fork.c b/kernel/fork.c
index 03c1eaaa6ef5..cfa84971fb52 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1592,6 +1592,22 @@ static struct task_struct *copy_process(unsigned long clone_flags,
syscall_tracepoint_update(p);
write_unlock_irq(&tasklist_lock);
+ /*
+ * If we have a new PGD then initialize it:
+ *
+ * This method is called after a task has been made visible
+ * on the task list already.
+ *
+ * Architectures that manage per task kernel pagetables
+ * might use this callback to initialize them after they
+ * are already visible to new updates.
+ *
+ * NOTE: any user-space parts of the PGD are already initialized
+ * and must not be clobbered.
+ */
+ if (!(clone_flags & CLONE_VM))
+ arch_pgd_init_late(p->mm);
+
proc_fork_connector(p);
cgroup_post_fork(p);
if (clone_flags & CLONE_THREAD)
--
2.1.4
--
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