Re: [PATCH v6 08/12] fork: Clear PASID for new mm
From: Jean-Philippe Brucker <hidden>
Date: 2021-02-24 10:20:43
Also in:
linux-iommu, lkml
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
quoted hunk
Signed-off-by: Fenghua Yu <redacted> Reviewed-by: Tony Luck <tony.luck@intel.com> --- 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