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Re: [PATCH] intel-iommu: Document iova_tree
From: |
Eric Auger |
Subject: |
Re: [PATCH] intel-iommu: Document iova_tree |
Date: |
Thu, 1 Dec 2022 19:17:41 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.1 |
Hi Peter
On 12/1/22 17:25, Peter Xu wrote:
> It seems not super clear on when iova_tree is used, and why. Add a rich
> comment above iova_tree to track why we needed the iova_tree, and when we
> need it.
>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> include/hw/i386/intel_iommu.h | 30 +++++++++++++++++++++++++++++-
> 1 file changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
> index 46d973e629..8d130ab2e3 100644
> --- a/include/hw/i386/intel_iommu.h
> +++ b/include/hw/i386/intel_iommu.h
> @@ -109,7 +109,35 @@ struct VTDAddressSpace {
> QLIST_ENTRY(VTDAddressSpace) next;
> /* Superset of notifier flags that this address space has */
> IOMMUNotifierFlag notifier_flags;
> - IOVATree *iova_tree; /* Traces mapped IOVA ranges */
> + /*
> + * @iova_tree traces mapped IOVA ranges.
> + *
> + * The tree is not needed if no MAP notifiers is registered with
s/no MAP notifiers/no MAP notifier
> + * current VTD address space, because all UNMAP (including iotlb or
> + * dev-iotlb) events can be transparently delivered to !MAP iommu
> + * notifiers.
because all UNMAP notifications (iotlb or dev-iotlb) can be triggered
directly, as opposed to MAP notifications. (?)
> + *
> + * The tree OTOH is required for MAP typed iommu notifiers for a few
> + * reasons.
> + *
> + * Firstly, there's no way to identify whether an PSI event is MAP or
maybe give the decryption of the 'PSI' and 'DSI" acronyms once ;-)
> + * UNMAP within the PSI message itself. Without having prior knowledge
> + * of existing state vIOMMU doesn't know whether it should notify MAP
> + * or UNMAP for a PSI message it received.
> + *
> + * Secondly, PSI received from guest driver (or even a large PSI can
> + * grow into a DSI at least with Linux intel-iommu driver) can be
> + * larger in range than the newly mapped ranges for either MAP or UNMAP
> + * events. If it directly pass-throughs any such event it may confuse
If it directly notifies the registered device with the unmodified range, it may
confuse the drivers ../..
So the range of the MAP notification can be adapted based on the existing IOVA
mappings.
> + * the registered drivers (e.g. vfio-pci) on either: (1) trying to map
> + * the same region more than once (for VFIO_IOMMU_MAP_DMA, -EEXIST will
> + * trigger), or (2) trying to UNMAP a range that is still partially
> + * mapped. That accuracy is not required for UNMAP-only notifiers, but
> + * it is a must-to-have for MAP-inclusive notifiers, because the vIOMMU
> + * needs to make sure the shadow page table is always in sync with the
> + * guest IOMMU pgtables for a device.
> + */
> + IOVATree *iova_tree;
> };
>
> struct VTDIOTLBEntry {
Thanks
Eric