Re: [Qemu-devel] [PATCH v14 09/22] vfio iommu type1: Add task structure to vfio_dma

[Alexey Kardashevskiy]

On 17/11/16 07:46, Kirti Wankhede wrote:
> Add task structure to vfio_dma structure. Task structure is used for:
> - During DMA_UNMAP, same task who mapped it or other task who shares same
> address space is allowed to unmap, otherwise unmap fails.
> QEMU maps few iova ranges initially, then fork threads and from the child
> thread calls DMA_UNMAP on previously mapped iova. Since child shares same
> address space, DMA_UNMAP is successful.
> - Avoid accessing struct mm while process is exiting by acquiring
> reference of task's mm during page accounting.
> - It is also used to get task mlock capability and rlimit for mlock.
> 
> Signed-off-by: Kirti Wankhede <address@hidden>
> Signed-off-by: Neo Jia <address@hidden>
> Reviewed-by: Dong Jia Shi <address@hidden>


I keep whinging that @mm should be referenced, not @current but you keep
referencing @current even if you only need @mm and you are not telling why
- and I am wondering what I am missing here? Something else will be used
from @task later, besides just @mm?


> 
> Change-Id: I7600f1bea6b384fd589fa72421ccf031bcfd9ac5
> ---
>  drivers/vfio/vfio_iommu_type1.c | 137 
> +++++++++++++++++++++++++---------------
>  1 file changed, 86 insertions(+), 51 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index ffe2026f1341..a0a7484cec64 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -36,6 +36,7 @@
>  #include <linux/uaccess.h>
>  #include <linux/vfio.h>
>  #include <linux/workqueue.h>
> +#include <linux/pid_namespace.h>
>  
>  #define DRIVER_VERSION  "0.2"
>  #define DRIVER_AUTHOR   "Alex Williamson <address@hidden>"
> @@ -75,6 +76,7 @@ struct vfio_dma {
>       unsigned long           vaddr;          /* Process virtual addr */
>       size_t                  size;           /* Map size (bytes) */
>       int                     prot;           /* IOMMU_READ/WRITE */
> +     struct task_struct      *task;
>  };
>  
>  struct vfio_group {
> @@ -277,41 +279,47 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned 
> long vaddr,
>   * the iommu can only map chunks of consecutive pfns anyway, so get the
>   * first page and all consecutive pages with the same locking.
>   */
> -static long vfio_pin_pages_remote(unsigned long vaddr, long npage,
> -                               int prot, unsigned long *pfn_base)
> +static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> +                               long npage, int prot, unsigned long *pfn_base)
>  {
> -     unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> -     bool lock_cap = capable(CAP_IPC_LOCK);
> +     unsigned long limit;
> +     bool lock_cap = ns_capable(task_active_pid_ns(dma->task)->user_ns,
> +                                CAP_IPC_LOCK);
> +     struct mm_struct *mm;
>       long ret, i;
>       bool rsvd;
>  
> -     if (!current->mm)
> +     mm = get_task_mm(dma->task);
> +     if (!mm)
>               return -ENODEV;
>  
> -     ret = vaddr_get_pfn(current->mm, vaddr, prot, pfn_base);
> +     ret = vaddr_get_pfn(mm, vaddr, prot, pfn_base);
>       if (ret)
> -             return ret;
> +             goto pin_pg_remote_exit;
>  
>       rsvd = is_invalid_reserved_pfn(*pfn_base);
> +     limit = task_rlimit(dma->task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
>  
> -     if (!rsvd && !lock_cap && current->mm->locked_vm + 1 > limit) {
> +     if (!rsvd && !lock_cap && mm->locked_vm + 1 > limit) {
>               put_pfn(*pfn_base, prot);
>               pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n", __func__,
>                       limit << PAGE_SHIFT);
> -             return -ENOMEM;
> +             ret = -ENOMEM;
> +             goto pin_pg_remote_exit;
>       }
>  
>       if (unlikely(disable_hugepages)) {
>               if (!rsvd)
> -                     vfio_lock_acct(current, 1);
> -             return 1;
> +                     vfio_lock_acct(dma->task, 1);
> +             ret = 1;
> +             goto pin_pg_remote_exit;
>       }
>  
>       /* Lock all the consecutive pages from pfn_base */
>       for (i = 1, vaddr += PAGE_SIZE; i < npage; i++, vaddr += PAGE_SIZE) {
>               unsigned long pfn = 0;
>  
> -             ret = vaddr_get_pfn(current->mm, vaddr, prot, &pfn);
> +             ret = vaddr_get_pfn(mm, vaddr, prot, &pfn);
>               if (ret)
>                       break;
>  
> @@ -321,8 +329,7 @@ static long vfio_pin_pages_remote(unsigned long vaddr, 
> long npage,
>                       break;
>               }
>  
> -             if (!rsvd && !lock_cap &&
> -                 current->mm->locked_vm + i + 1 > limit) {
> +             if (!rsvd && !lock_cap && mm->locked_vm + i + 1 > limit) {
>                       put_pfn(pfn, prot);
>                       pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
>                               __func__, limit << PAGE_SHIFT);
> @@ -331,13 +338,16 @@ static long vfio_pin_pages_remote(unsigned long vaddr, 
> long npage,
>       }
>  
>       if (!rsvd)
> -             vfio_lock_acct(current, i);
> +             vfio_lock_acct(dma->task, i);
> +     ret = i;
>  
> -     return i;
> +pin_pg_remote_exit:
> +     mmput(mm);
> +     return ret;
>  }
>  
> -static long vfio_unpin_pages_remote(unsigned long pfn, long npage,
> -                                 int prot, bool do_accounting)
> +static long vfio_unpin_pages_remote(struct vfio_dma *dma, unsigned long pfn,
> +                                 long npage, int prot, bool do_accounting)
>  {
>       unsigned long unlocked = 0;
>       long i;
> @@ -346,7 +356,7 @@ static long vfio_unpin_pages_remote(unsigned long pfn, 
> long npage,
>               unlocked += put_pfn(pfn++, prot);
>  
>       if (do_accounting)
> -             vfio_lock_acct(current, -unlocked);
> +             vfio_lock_acct(dma->task, -unlocked);
>  
>       return unlocked;
>  }
> @@ -400,7 +410,7 @@ static void vfio_unmap_unpin(struct vfio_iommu *iommu, 
> struct vfio_dma *dma)
>               if (WARN_ON(!unmapped))
>                       break;
>  
> -             unlocked += vfio_unpin_pages_remote(phys >> PAGE_SHIFT,
> +             unlocked += vfio_unpin_pages_remote(dma, phys >> PAGE_SHIFT,
>                                                   unmapped >> PAGE_SHIFT,
>                                                   dma->prot, false);
>               iova += unmapped;
> @@ -408,13 +418,14 @@ static void vfio_unmap_unpin(struct vfio_iommu *iommu, 
> struct vfio_dma *dma)
>               cond_resched();
>       }
>  
> -     vfio_lock_acct(current, -unlocked);
> +     vfio_lock_acct(dma->task, -unlocked);
>  }
>  
>  static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
>  {
>       vfio_unmap_unpin(iommu, dma);
>       vfio_unlink_dma(iommu, dma);
> +     put_task_struct(dma->task);
>       kfree(dma);
>  }
>  
> @@ -510,6 +521,12 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>       while ((dma = vfio_find_dma(iommu, unmap->iova, unmap->size))) {
>               if (!iommu->v2 && unmap->iova > dma->iova)
>                       break;
> +             /*
> +              * Task with same address space who mapped this iova range is
> +              * allowed to unmap the iova range.
> +              */
> +             if (dma->task->mm != current->mm)
> +                     break;
>               unmapped += dma->size;
>               vfio_remove_dma(iommu, dma);
>       }
> @@ -576,17 +593,55 @@ unwind:
>       return ret;
>  }
>  
> +static int vfio_pin_map_dma(struct vfio_iommu *iommu, struct vfio_dma *dma,
> +                         size_t map_size)
> +{
> +     dma_addr_t iova = dma->iova;
> +     unsigned long vaddr = dma->vaddr;
> +     size_t size = map_size;
> +     long npage;
> +     unsigned long pfn;
> +     int ret = 0;
> +
> +     while (size) {
> +             /* Pin a contiguous chunk of memory */
> +             npage = vfio_pin_pages_remote(dma, vaddr + dma->size,
> +                                           size >> PAGE_SHIFT, dma->prot,
> +                                           &pfn);
> +             if (npage <= 0) {
> +                     WARN_ON(!npage);
> +                     ret = (int)npage;
> +                     break;
> +             }
> +
> +             /* Map it! */
> +             ret = vfio_iommu_map(iommu, iova + dma->size, pfn, npage,
> +                                  dma->prot);
> +             if (ret) {
> +                     vfio_unpin_pages_remote(dma, pfn, npage,
> +                                              dma->prot, true);
> +                     break;
> +             }
> +
> +             size -= npage << PAGE_SHIFT;
> +             dma->size += npage << PAGE_SHIFT;
> +     }
> +
> +     if (ret)
> +             vfio_remove_dma(iommu, dma);
> +
> +     return ret;
> +}
> +
>  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;
>  
>       /* Verify that none of our __u64 fields overflow */
>       if (map->size != size || map->vaddr != vaddr || map->iova != iova)
> @@ -612,47 +667,27 @@ 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 out_unlock;
>       }
>  
>       dma = kzalloc(sizeof(*dma), GFP_KERNEL);
>       if (!dma) {
> -             mutex_unlock(&iommu->lock);
> -             return -ENOMEM;
> +             ret = -ENOMEM;
> +             goto out_unlock;
>       }
>  
>       dma->iova = iova;
>       dma->vaddr = vaddr;
>       dma->prot = prot;
> +     get_task_struct(current);
> +     dma->task = current;
>  
>       /* Insert zero-sized and grow as we map chunks of it */
>       vfio_link_dma(iommu, dma);
>  
> -     while (size) {
> -             /* Pin a contiguous chunk of memory */
> -             npage = vfio_pin_pages_remote(vaddr + dma->size,
> -                                           size >> PAGE_SHIFT, prot, &pfn);
> -             if (npage <= 0) {
> -                     WARN_ON(!npage);
> -                     ret = (int)npage;
> -                     break;
> -             }
> -
> -             /* Map it! */
> -             ret = vfio_iommu_map(iommu, iova + dma->size, pfn, npage, prot);
> -             if (ret) {
> -                     vfio_unpin_pages_remote(pfn, npage, prot, true);
> -                     break;
> -             }
> -
> -             size -= npage << PAGE_SHIFT;
> -             dma->size += npage << PAGE_SHIFT;
> -     }
> -
> -     if (ret)
> -             vfio_remove_dma(iommu, dma);
> -
> +     ret = vfio_pin_map_dma(iommu, dma, size);
> +out_unlock:
>       mutex_unlock(&iommu->lock);
>       return ret;
>  }
> 


-- 
Alexey