On 10/29/2016 2:03 AM, Alex Williamson wrote:
> On Sat, 29 Oct 2016 01:32:35 +0530
> Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
>
>> On 10/28/2016 6:10 PM, Alex Williamson wrote:
>>> On Fri, 28 Oct 2016 15:33:58 +0800
>>> Jike Song <jike.song@xxxxxxxxx> wrote:
>>>
...
>>>>>
>>>>> +/*
>>>>> + * This function finds pfn in domain->external_addr_space->pfn_list for given
>>>>> + * iova range. If pfn exist, notify pfn to registered notifier list. On
>>>>> + * receiving notifier callback, vendor driver should invalidate the mapping and
>>>>> + * call vfio_unpin_pages() to unpin this pfn. With that vfio_pfn for this pfn
>>>>> + * gets removed from rb tree of pfn_list. That re-arranges rb tree, so while
>>>>> + * searching for next vfio_pfn in rb tree, start search from first node again.
>>>>> + * If any vendor driver doesn't unpin that pfn, vfio_pfn would not get removed
>>>>> + * from rb tree and so in next search vfio_pfn would be same as previous
>>>>> + * vfio_pfn. In that case, exit from loop.
>>>>> + */
>>>>> +static void vfio_notifier_call_chain(struct vfio_iommu *iommu,
>>>>> + struct vfio_iommu_type1_dma_unmap *unmap)
>>>>> +{
>>>>> + struct vfio_domain *domain = iommu->external_domain;
>>>>> + struct rb_node *n;
>>>>> + struct vfio_pfn *vpfn = NULL, *prev_vpfn;
>>>>> +
>>>>> + do {
>>>>> + prev_vpfn = vpfn;
>>>>> + mutex_lock(&domain->external_addr_space->pfn_list_lock);
>>>>> +
>>>>> + n = rb_first(&domain->external_addr_space->pfn_list);
>>>>> +
>>>>> + for (; n; n = rb_next(n), vpfn = NULL) {
>>>>> + vpfn = rb_entry(n, struct vfio_pfn, node);
>>>>> +
>>>>> + if ((vpfn->iova >= unmap->iova) &&
>>>>> + (vpfn->iova < unmap->iova + unmap->size))
>>>>> + break;
>>>>> + }
>>>>> +
>>>>> + mutex_unlock(&domain->external_addr_space->pfn_list_lock);
>>>>> +
>>>>> + /* Notify any listeners about DMA_UNMAP */
>>>>> + if (vpfn)
>>>>> + blocking_notifier_call_chain(&iommu->notifier,
>>>>> + VFIO_IOMMU_NOTIFY_DMA_UNMAP,
>>>>> + &vpfn->pfn);
>>>>
>>>> Hi Kirti,
>>>>
>>>> The information carried by notifier is only a pfn.
>>>>
>>>> Since your pin/unpin interfaces design, it's the vendor driver who should
>>>> guarantee pin/unpin same times. To achieve that, the vendor driver must
>>>> cache it's iova->pfn mapping on its side, to avoid pinning a same page
>>>> for multiple times.
>>>>
>>>> With the notifier carrying only a pfn, to find the iova by this pfn,
>>>> the vendor driver must *also* keep a reverse-mapping. That's a bit
>>>> too much.
>>>>
>>>> Since the vendor could also suffer from IOMMU-compatible problem,
>>>> which means a local cache is always helpful, so I'd like to have the
>>>> iova carried to the notifier.
>>>>
>>>> What'd you say?
>>>
>>> I agree, the pfn is not unique, multiple guest pfns (iovas) might be
>>> backed by the same host pfn. DMA_UNMAP calls are based on iova, the
>>> notifier through to the vendor driver must be based on the same.
>>
>> Host pfn should be unique, right?
>
> Let's say a user does a malloc of a single page and does 100 calls to
> MAP_DMA populating 100 pages of IOVA space all backed by the same
> malloc'd page. This is valid, I have unit tests that do essentially
> this. Those will all have the same pfn. The user then does an
> UNMAP_DMA to a single one of those IOVA pages. Did the user unmap
> everything matching that pfn? Of course not, they only unmapped that
> one IOVA page. There is no guarantee of a 1:1 mapping of pfn to IOVA.
> UNMAP_DMA works based on IOVA. Invalidation broadcasts to the vendor
> driver MUST therefore also work based on IOVA. This is not an academic
> problem, address space aliases exist in real VMs, imagine a virtual
> IOMMU. Thanks,
>
So struct vfio_iommu_type1_dma_unmap should be passed as argument to
notifier callback:
if (unmapped && iommu->external_domain)
- vfio_notifier_call_chain(iommu, unmap);
+ blocking_notifier_call_chain(&iommu->notifier,
+ VFIO_IOMMU_NOTIFY_DMA_UNMAP,
+ unmap);
Then vendor driver should find pfns he has pinned from this range of
iovas, then invalidate and unpin pfns. Right?
Thanks,
Kirti
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