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SubjectRe: [PATCH 1/5] vfio/type1: use pinned_vm instead of locked_vm to account pinned pages
On Mon, Feb 11, 2019 at 05:44:33PM -0500, Daniel Jordan wrote:
> Beginning with bc3e53f682d9 ("mm: distinguish between mlocked and pinned
> pages"), locked and pinned pages are accounted separately. Type1
> accounts pinned pages to locked_vm; use pinned_vm instead.
>
> pinned_vm recently became atomic and so no longer relies on mmap_sem
> held as writer: delete.
>
> Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
> drivers/vfio/vfio_iommu_type1.c | 31 ++++++++++++-------------------
> 1 file changed, 12 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 73652e21efec..a56cc341813f 100644
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -257,7 +257,8 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
> static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
> {
> struct mm_struct *mm;
> - int ret;
> + s64 pinned_vm;
> + int ret = 0;
>
> if (!npage)
> return 0;
> @@ -266,24 +267,15 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
> if (!mm)
> return -ESRCH; /* process exited */
>
> - ret = down_write_killable(&mm->mmap_sem);
> - if (!ret) {
> - if (npage > 0) {
> - if (!dma->lock_cap) {
> - unsigned long limit;
> -
> - limit = task_rlimit(dma->task,
> - RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> + pinned_vm = atomic64_add_return(npage, &mm->pinned_vm);
>
> - if (mm->locked_vm + npage > limit)
> - ret = -ENOMEM;
> - }
> + if (npage > 0 && !dma->lock_cap) {
> + unsigned long limit = task_rlimit(dma->task, RLIMIT_MEMLOCK) >>
> +
> - PAGE_SHIFT;

I haven't looked at this super closely, but how does this stuff work?

do_mlock doesn't touch pinned_vm, and this doesn't touch locked_vm...

Shouldn't all this be 'if (locked_vm + pinned_vm < RLIMIT_MEMLOCK)' ?

Otherwise MEMLOCK is really doubled..

Jason

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