Re: [PATCH v4 1/2] vfio/type1: Remove locked page accounting workqueue

Peter Xu
2017-04-17T06:48:07Z

On Sun, Apr 16, 2017 at 07:42:27PM -0600, Alex Williamson wrote:

[...]

> -static void vfio_lock_acct(struct task_struct *task, long npage)
> +static int vfio_lock_acct(struct task_struct *task, long npage, bool lock_cap)
> {
> - struct vwork *vwork;
> struct mm_struct *mm;
> bool is_current;
> + int ret;
>
> if (!npage)
> - return;
> + return 0;
>
> is_current = (task->mm == current->mm);
>
> mm = is_current ? task->mm : get_task_mm(task);
> if (!mm)
> - return; /* process exited */
> + return -ESRCH; /* process exited */
>
> - if (down_write_trylock(&mm->mmap_sem)) {
> - mm->locked_vm += npage;
> - up_write(&mm->mmap_sem);
> - if (!is_current)
> - mmput(mm);
> - return;
> - }
> + ret = down_write_killable(&mm->mmap_sem);
> + if (!ret) {
> + if (npage < 0 || lock_cap) {

Nit: maybe we can avoid passing in lock_cap in all the callers of
vfio_lock_acct() and fetch it via has_capability() only if npage < 0?
IMHO that'll keep the vfio_lock_acct() interface cleaner, and we won't
need to pass in "false" any time when doing unpins.

[...]

> @@ -405,7 +379,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> long npage, unsigned long *pfn_base)
> {
> - unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> + unsigned long pfn = 0, limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> bool lock_cap = capable(CAP_IPC_LOCK);
> long ret, pinned = 0, lock_acct = 0;
> bool rsvd;
> @@ -442,8 +416,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> /* Lock all the consecutive pages from pfn_base */
> for (vaddr += PAGE_SIZE, iova += PAGE_SIZE; pinned < npage;
> pinned++, vaddr += PAGE_SIZE, iova += PAGE_SIZE) {
> - unsigned long pfn = 0;
> -
> ret = vaddr_get_pfn(current->mm, vaddr, dma->prot, &pfn);
> if (ret)
> break;
> @@ -460,14 +432,25 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
> put_pfn(pfn, dma->prot);
> pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n",
> __func__, limit << PAGE_SHIFT);
> - break;
> + ret = -ENOMEM;
> + goto unpin_out;
> }
> lock_acct++;
> }
> }
>
> out:
> - vfio_lock_acct(current, lock_acct);
> + ret = vfio_lock_acct(current, lock_acct, lock_cap);

I just didn't notice this in previous review, but... do we need to
check against !rsvd as well here before doing the accounting?

Thanks!

> +
> +unpin_out:
> + if (ret) {
> + if (!rsvd) {
> + for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
> + put_pfn(pfn, dma->prot);
> + }
> +
> + return ret;
> + }
>
> return pinned;
> }

--
Peter Xu