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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id n29-20020a05600c3b9d00b003c21ba7d7d6sm24578656wms.44.2022.12.06.05.16.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 06 Dec 2022 05:16:33 -0800 (PST) Message-ID: <6189ef29-fe38-bc74-aff1-034eb28ab031@redhat.com> Date: Tue, 6 Dec 2022 14:16:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.1 Subject: Re: [PATCH] intel-iommu: Document iova_tree Content-Language: en-US To: Peter Xu , Jason Wang Cc: qemu-devel@nongnu.org, "Michael S . Tsirkin" , Yi Liu , Alex Williamson References: <20221201162501.3864692-1-peterx@redhat.com> From: Eric Auger In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=eric.auger@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 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, NICE_REPLY_A=-0.27, RCVD_IN_DNSWL_LOW=-0.7, 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: , Reply-To: eric.auger@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org 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. > + * 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' > + * 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