On 09/30/2016 10:58 AM, Jike Song wrote:
> On 09/29/2016 11:06 PM, Kirti Wankhede wrote:
>>
>>
>> On 9/29/2016 7:47 AM, Jike Song wrote:
>>> +Guangrong
>>>
>>> On 08/25/2016 11:53 AM, Kirti Wankhede wrote:
>>
>> ...
>>
>>>> +static long vfio_iommu_type1_pin_pages(void *iommu_data,
>>>> + unsigned long *user_pfn,
>>>> + long npage, int prot,
>>>> + unsigned long *phys_pfn)
>>>> +{
>>>> + struct vfio_iommu *iommu = iommu_data;
>>>> + struct vfio_domain *domain;
>>>> + int i, j, ret;
>>>> + long retpage;
>>>> + unsigned long remote_vaddr;
>>>> + unsigned long *pfn = phys_pfn;
>>>> + struct vfio_dma *dma;
>>>> + bool do_accounting = false;
>>>> +
>>>> + if (!iommu || !user_pfn || !phys_pfn)
>>>> + return -EINVAL;
>>>> +
>>>> + mutex_lock(&iommu->lock);
>>>> +
>>>> + if (!iommu->local_domain) {
>>>> + ret = -EINVAL;
>>>> + goto pin_done;
>>>> + }
>>>> +
>>>> + domain = iommu->local_domain;
>>>> +
>>>> + /*
>>>> + * If iommu capable domain exist in the container then all pages are
>>>> + * already pinned and accounted. Accouting should be done if there is no
>>>> + * iommu capable domain in the container.
>>>> + */
>>>> + do_accounting = !IS_IOMMU_CAPABLE_DOMAIN_IN_CONTAINER(iommu);
>>>> +
>>>> + for (i = 0; i < npage; i++) {
>>>> + struct vfio_pfn *p;
>>>> + dma_addr_t iova;
>>>> +
>>>> + iova = user_pfn[i] << PAGE_SHIFT;
>>>> +
>>>> + dma = vfio_find_dma(iommu, iova, 0);
>>>> + if (!dma) {
>>>> + ret = -EINVAL;
>>>> + goto pin_unwind;
>>>> + }
>>>> +
>>>> + remote_vaddr = dma->vaddr + iova - dma->iova;
>>>> +
>>>> + retpage = __vfio_pin_pages_local(domain, remote_vaddr, prot,
>>>> + &pfn[i], do_accounting);
>>>
>>> Hi Kirti,
>>>
>>> Here you call __vfio_pin_pages_local() > vaddr_get_pfn() > GUP regardless
>>> whether the vaddr already pinned or not. That probably means, if the caller
>>> calls vfio_pin_pages() with a GPA for multiple times, you get memory leaks.
>>>
>>> GUP always increases the page refcnt.
>>>
>>> FWIW, I would like to have the pfn_list_lock implemented with key == iova,
>>> so you can always try to find the PFN for a given iova, and pin it only if
>>> not found.
>>>
>>
>> I didn't get how there would be a memory leak.
>>
>> Right, GUP increases refcnt, so if vfio_pin_pages() is called for
>> multiple types for same GPA, refcnt would be incremented. In
>> vfio_iommu_type1_pin_pages() pinned pages list is maintained with
>> ref_count. If pfn is already in list, ref_count is incremented and same
>> is used while unpining pages.
>>
>
> Let's have a close look at vfio_unpin_pfn:
>
> static int vfio_unpin_pfn(struct vfio_domain *domain,
> struct vfio_pfn *vpfn, bool do_accounting)
> {
> __vfio_unpin_pages_for_mdev(domain, vpfn->pfn, vpfn->prot,
> do_accounting);
>
> if (atomic_dec_and_test(&vpfn->ref_count))
> vfio_remove_from_pfn_list(domain, vpfn);
>
> return 1;
> }
>
> Here you didn't call __vfio_unpin_pages_for_mdev -- thereby put_page -- for
> vpfn->ref_count times. If page->_refcount increased by GUP for (N) times, here
> you only set it back to (N-1).
>
What's more, since all pinned {iova, pfni} already saved, it's better to
consult it before calling GUP, which will get_page() unconditionally.
--
Thanks,
Jike
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