On Tue, 8 Nov 2016 19:43:25 +0530
Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
> On 11/8/2016 2:33 AM, Alex Williamson wrote:
> > On Sat, 5 Nov 2016 02:40:43 +0530
> > Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
> >
>
> ...
>
> >> static int vfio_dma_do_map(struct vfio_iommu *iommu,
> >> struct vfio_iommu_type1_dma_map *map)
> >> {
> >> dma_addr_t iova = map->iova;
> >> unsigned long vaddr = map->vaddr;
> >> size_t size = map->size;
> >> - long npage;
> >> int ret = 0, prot = 0;
> >> uint64_t mask;
> >> struct vfio_dma *dma;
> >> - unsigned long pfn;
> >> + struct vfio_addr_space *addr_space;
> >> + struct mm_struct *mm;
> >> + bool free_addr_space_on_err = false;
> >>
> >> /* Verify that none of our __u64 fields overflow */
> >> if (map->size != size || map->vaddr != vaddr || map->iova != iova)
> >> @@ -608,47 +685,56 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
> >> mutex_lock(&iommu->lock);
> >>
> >> if (vfio_find_dma(iommu, iova, size)) {
> >> - mutex_unlock(&iommu->lock);
> >> - return -EEXIST;
> >> + ret = -EEXIST;
> >> + goto do_map_err;
> >> + }
> >> +
> >> + mm = get_task_mm(current);
> >> + if (!mm) {
> >> + ret = -ENODEV;
> >
> > -EFAULT?
> >
>
> -ENODEV return is in original code from vfio_pin_pages()
> if (!current->mm)
> return -ENODEV;
>
> Once I thought of changing it to -EFAULT, but then again changed to
> -ENODEV to be consistent with original error code.
>
> Should I still change this return to -EFAULT?
Let's keep ENODEV for less code churn, I guess.
> >> + goto do_map_err;
> >> + }
> >> +
> >> + addr_space = vfio_find_addr_space(iommu, mm);
> >> + if (addr_space) {
> >> + atomic_inc(&addr_space->ref_count);
> >> + mmput(mm);
> >> + } else {
> >> + addr_space = kzalloc(sizeof(*addr_space), GFP_KERNEL);
> >> + if (!addr_space) {
> >> + ret = -ENOMEM;
> >> + goto do_map_err;
> >> + }
> >> + addr_space->mm = mm;
> >> + atomic_set(&addr_space->ref_count, 1);
> >> + list_add(&addr_space->next, &iommu->addr_space_list);
> >> + free_addr_space_on_err = true;
> >> }
> >>
> >> dma = kzalloc(sizeof(*dma), GFP_KERNEL);
> >> if (!dma) {
> >> - mutex_unlock(&iommu->lock);
> >> - return -ENOMEM;
> >> + if (free_addr_space_on_err) {
> >> + mmput(mm);
> >> + list_del(&addr_space->next);
> >> + kfree(addr_space);
> >> + }
> >> + ret = -ENOMEM;
> >> + goto do_map_err;
> >> }
> >>
> >> dma->iova = iova;
> >> dma->vaddr = vaddr;
> >> dma->prot = prot;
> >> + dma->addr_space = addr_space;
> >> + get_task_struct(current);
> >> + dma->task = current;
> >> + dma->mlock_cap = capable(CAP_IPC_LOCK);
> >
> >
> > How do you reason we can cache this? Does the fact that the process
> > had this capability at the time that it did a DMA_MAP imply that it
> > necessarily still has this capability when an external user (vendor
> > driver) tries to pin pages? I don't see how we can make that
> > assumption.
> >
> >
>
> Will process change MEMLOCK limit at runtime? I think it shouldn't,
> correct me if I'm wrong. QEMU doesn't do that, right?
What QEMU does or doesn't do isn't relevant, the question is could a
process change CAP_IPC_LOCK runtime. It seems plausible to me.
> The function capable() determines current task's capability. But when
> vfio_pin_pages() is called, it could come from other task but pages are
> pinned from address space of task who mapped it. So we can't use
> capable() in vfio_pin_pages()
>
> If this capability shouldn't be cached, we have to use has_capability()
> with dma->task as argument in vfio_pin_pages()
>
> bool has_capability(struct task_struct *t, int cap)
Yep, that sounds better. Thanks,
Alex
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