Re: [PATCH v6 08/12] fork: Clear PASID for new mm
From: Jean-Philippe Brucker
Date: Wed Feb 24 2021 - 05:20:42 EST
Hi Fenghua,
[Trimmed the Cc list]
On Mon, Jul 13, 2020 at 04:48:03PM -0700, Fenghua Yu wrote:
>
When a new mm is created, its PASID should be cleared, i.e. the PASID is
>
initialized to its init state 0 on both ARM and X86.
I just noticed this patch was dropped in v7, and am wondering whether we
could still upstream it. Does x86 need a child with a new address space
(!CLONE_VM) to inherit the PASID of the parent? That doesn't make much
sense with regard to IOMMU structures - same PASID indexing multiple PGDs?
Currently iommu_sva_alloc_pasid() assumes mm->pasid is always initialized
to 0 and fails on forked tasks. I'm trying to figure out how to fix this.
Could we clear the pasid on fork or does it break the x86 model?
Thanks,
Jean
>
>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
>
---
>
v2:
>
- Add this patch to initialize PASID value for a new mm.
>
>
include/linux/mm_types.h | 2 ++
>
kernel/fork.c | 8 ++++++++
>
2 files changed, 10 insertions(+)
>
>
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
>
index d61285cfe027..d60d2ec10881 100644
>
--- a/include/linux/mm_types.h
>
+++ b/include/linux/mm_types.h
>
@@ -22,6 +22,8 @@
>
#endif
>
#define AT_VECTOR_SIZE (2*(AT_VECTOR_SIZE_ARCH + AT_VECTOR_SIZE_BASE + 1))
>
>
+/* Initial PASID value is 0. */
>
+#define INIT_PASID 0
>
>
struct address_space;
>
struct mem_cgroup;
>
diff --git a/kernel/fork.c b/kernel/fork.c
>
index 142b23645d82..43b5f112604d 100644
>
--- a/kernel/fork.c
>
+++ b/kernel/fork.c
>
@@ -1007,6 +1007,13 @@ 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_SUPPORT
>
+ mm->pasid = INIT_PASID;
>
+#endif
>
+}
>
+
>
static void mm_init_uprobes_state(struct mm_struct *mm)
>
{
>
#ifdef CONFIG_UPROBES
>
@@ -1035,6 +1042,7 @@ 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);
>
RCU_INIT_POINTER(mm->exe_file, NULL);
>
mmu_notifier_subscriptions_init(mm);
>
init_tlb_flush_pending(mm);
>
--
>
2.19.1
>