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Tue, 30 Jun 2020 08:29:20 +0000 (UTC) Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier From: Jason Wang To: Peter Xu References: <20200626064122.9252-1-eperezma@redhat.com> <20200626064122.9252-2-eperezma@redhat.com> <20200626212917.GD175520@xz-x1> <8cf25190-53e6-8cbb-372b-e3d4ec714dc5@redhat.com> <20200628144746.GA239443@xz-x1> <54d2cdfd-97b8-9e1d-a607-d7a5e96be3a1@redhat.com> <20200629133403.GA266532@xz-x1> <2589d0e9-cc5b-a4df-8790-189b49f1a40e@redhat.com> Message-ID: <1b4eaaaf-c2ab-0da8-afb4-1b7b4221e6cf@redhat.com> Date: Tue, 30 Jun 2020 16:29:19 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <2589d0e9-cc5b-a4df-8790-189b49f1a40e@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; 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Tsirkin" , qemu-devel@nongnu.org, =?UTF-8?Q?Eugenio_P=c3=a9rez?= , Eric Auger , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/6/30 上午10:41, Jason Wang wrote: > > On 2020/6/29 下午9:34, Peter Xu wrote: >> On Mon, Jun 29, 2020 at 01:51:47PM +0800, Jason Wang wrote: >>> On 2020/6/28 下午10:47, Peter Xu wrote: >>>> On Sun, Jun 28, 2020 at 03:03:41PM +0800, Jason Wang wrote: >>>>> On 2020/6/27 上午5:29, Peter Xu wrote: >>>>>> Hi, Eugenio, >>>>>> >>>>>> (CCing Eric, Yan and Michael too) >>>>>> >>>>>> On Fri, Jun 26, 2020 at 08:41:22AM +0200, Eugenio Pérez wrote: >>>>>>> diff --git a/memory.c b/memory.c >>>>>>> index 2f15a4b250..7f789710d2 100644 >>>>>>> --- a/memory.c >>>>>>> +++ b/memory.c >>>>>>> @@ -1915,8 +1915,6 @@ void >>>>>>> memory_region_notify_one(IOMMUNotifier *notifier, >>>>>>>             return; >>>>>>>         } >>>>>>> -    assert(entry->iova >= notifier->start && entry_end <= >>>>>>> notifier->end); >>>>>> I can understand removing the assertion should solve the issue, >>>>>> however imho >>>>>> the major issue is not about this single assertion but the whole >>>>>> addr_mask >>>>>> issue behind with virtio... >>>>> I don't get here, it looks to the the range was from guest IOMMU >>>>> drivers. >>>> Yes.  Note that I didn't mean that it's a problem in virtio, it's >>>> just the fact >>>> that virtio is the only one I know that would like to support >>>> arbitrary address >>>> range for the translated region.  I don't know about tcg, but vfio >>>> should still >>>> need some kind of page alignment in both the address and the >>>> addr_mask.  We >>>> have that assumption too across the memory core when we do >>>> translations. >>> >>> Right but it looks to me the issue is not the alignment. >>> >>> >>>> A further cause of the issue is the MSI region when vIOMMU enabled >>>> - currently >>>> we implemented the interrupt region using another memory region so >>>> it split the >>>> whole DMA region into two parts.  That's really a clean approach to IR >>>> implementation, however that's also a burden to the invalidation >>>> part because >>>> then we'll need to handle things like this when the listened range >>>> is not page >>>> alighed at all (neither 0-0xfedffff, nor 0xfef0000-MAX).  If >>>> without the IR >>>> region (so the whole iommu address range will be a single FlatRange), >>> >>> Is this a bug? I remember that at least for vtd, it won't do any >>> DMAR on the >>> intrrupt address range >> I don't think it's a bug, at least it's working as how I >> understand...  that >> interrupt range is using an IR region, that's why I said the IR >> region splits >> the DMAR region into two pieces, so we have two FlatRange for the same >> IOMMUMemoryRegion. > > > I don't check the qemu code but if "a single FlatRange" means > 0xFEEx_xxxx is subject to DMA remapping, OS need to setup passthrough > mapping for that range in order to get MSI to work. This is not what > vtd spec said: > > """ > > 3.14 Handling Requests to Interrupt Address Range > > Requests without PASID to address range 0xFEEx_xxxx are treated as > potential interrupt requests and are not subjected to DMA remapping > (even if translation structures specify a mapping for this > range). Instead, remapping hardware can be enabled to subject such > interrupt requests to interrupt remapping. > > """ > > My understanding is vtd won't do any DMA translation on 0xFEEx_xxxx > even if IR is not enabled. Ok, we had a dedicated mr for interrupt: memory_region_add_subregion_overlap(MEMORY_REGION(&vtd_dev_as->iommu), VTD_INTERRUPT_ADDR_FIRST, &vtd_dev_as->iommu_ir, 1); So it should be fine. I guess the reason that I'm asking is that I thought "IR" means "Interrupt remapping" but in fact it means "Interrupt Region"? But I'm still not clear about the invalidation part for interrupt region, maybe you can elaborate a little more on this. Btw, I think guest can trigger the assert in vtd_do_iommu_translate() if we teach vhost to DMA to that region:     /*      * We have standalone memory region for interrupt addresses, we      * should never receive translation requests in this region.      */     assert(!vtd_is_interrupt_addr(addr)); Is this better to return false here? (We can work on the fix for vhost but it should be not trivial) Thanks