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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id c23-20020a05620a269700b006e8f8ca8287sm15055524qkp.120.2022.12.06.08.05.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Dec 2022 08:05:07 -0800 (PST) Date: Tue, 6 Dec 2022 11:05:07 -0500 From: Peter Xu To: Eric Auger Cc: Jason Wang , qemu-devel@nongnu.org, "Michael S . Tsirkin" , Yi Liu , Alex Williamson Subject: Re: [PATCH] intel-iommu: Document iova_tree Message-ID: References: <20221201162501.3864692-1-peterx@redhat.com> <6189ef29-fe38-bc74-aff1-034eb28ab031@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6189ef29-fe38-bc74-aff1-034eb28ab031@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Dec 06, 2022 at 02:16:32PM +0100, Eric Auger wrote: > Hi Peter, > On 12/6/22 00:28, Peter Xu wrote: > > On Mon, Dec 05, 2022 at 12:23:20PM +0800, Jason Wang wrote: > >> On Fri, Dec 2, 2022 at 12:25 AM 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 > >>> Signed-off-by: Peter Xu > >>> --- > >>> 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 > >>> + * current VTD address space, because all UNMAP (including iotlb or > >>> + * dev-iotlb) events can be transparently delivered to !MAP iommu > >>> + * notifiers. > >> So this means the UNMAP notifier doesn't need to be as accurate as > >> MAP. (Should we document it in the notifier headers)? > > Yes. > > > >> For MAP[a, b] MAP[b, c] we can do a UNMAP[a. c]. > > IIUC a better way to say this is, for MAP[a, b] we can do an UNMAP[a-X, > > b+Y] as long as the range covers [a, b]? > > > >>> + * > >>> + * 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 > >>> + * 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. > >> Yes, so I think we need a document that the UNMAP handler should be > >> prepared for this. > > How about I squash below into this same patch? > > > > diff --git a/include/exec/memory.h b/include/exec/memory.h > > index 91f8a2395a..c83bd11a68 100644 > > --- a/include/exec/memory.h > > +++ b/include/exec/memory.h > > @@ -129,6 +129,24 @@ struct IOMMUTLBEntry { > > /* > > * Bitmap for different IOMMUNotifier capabilities. Each notifier can > > * register with one or multiple IOMMU Notifier capability bit(s). > > + * > > + * Normally there're two use cases for the notifiers: > > + * > > + * (1) When the device needs accurate synchronizations of the vIOMMU page > accurate synchronizations sound too vague & subjective to me. Suggestions? > > + * tables, it needs to register with both MAP|UNMAP notifies (which > > + * is defined as IOMMU_NOTIFIER_IOTLB_EVENTS below). As long as MAP > > + * events are registered, the notifications will be accurate but > > + * there's overhead on synchronizing the guest vIOMMU page tables. > > + * > > + * (2) When the device doesn't need accurate synchronizations of the > > + * vIOMMU page tables (when the device can both cache translations > > + * and requesting to translate dynamically during DMA process), it > s/requesting/request > > + * needs to register only with UNMAP or DEVIOTLB_UNMAP notifies. > would be nice to clarify the distinction between both then > > + * Note that in such working mode shadow page table is not used for > > + * vIOMMU unit on this address space, so the UNMAP messages can be > I do not catch 'is not used for vIOMMU unit on this address space' How about: "Note that in this working mode the vIOMMU will not maintain a shadowed page table for the address space, and the UNMAP messages can be.."? > > + * actually larger than the real invalidations (just like how the > > + * Linux IOMMU driver normally works, where an invalidation can be > > + * enlarged as long as it still covers the target range). > > */ > > typedef enum { > > IOMMU_NOTIFIER_NONE = 0, > > > > Thanks, > > > Thanks > > Eric > -- Peter Xu