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Wed, 1 Jul 2020 08:09:48 +0000 (UTC) Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier 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> <20200630153911.GD3138@xz-x1> From: Jason Wang Message-ID: <69f6d6e7-a0b1-abae-894e-4e81b7e0cc90@redhat.com> Date: Wed, 1 Jul 2020 16:09:46 +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: <20200630153911.GD3138@xz-x1> 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 下午11:39, Peter Xu wrote: > On Tue, Jun 30, 2020 at 10:41:10AM +0800, Jason Wang wrote: >>> /* According to ATS spec table 2.4: >>> * S = 0, bits 15:12 = xxxx range size: 4K >>> * S = 1, bits 15:12 = xxx0 range size: 8K >>> * S = 1, bits 15:12 = xx01 range size: 16K >>> * S = 1, bits 15:12 = x011 range size: 32K >>> * S = 1, bits 15:12 = 0111 range size: 64K >>> * ... >>> */ >> >> Right, but the comment is probably misleading here, since it's for the PCI-E >> transaction between IOMMU and device not for the device IOTLB invalidation >> descriptor. >> >> For device IOTLB invalidation descriptor, spec allows a [0, ~0ULL] >> invalidation: >> >> " >> >> 6.5.2.5 Device-TLB Invalidate Descriptor >> >> ... >> >> Size (S): The size field indicates the number of consecutive pages targeted >> by this invalidation >> request. If S field is zero, a single page at page address specified by >> Address [63:12] is requested >> to be invalidated. If S field is Set, the least significant bit in the >> Address field with value 0b >> indicates the invalidation address range. For example, if S field is Set and >> Address[12] is Clear, it >> indicates an 8KB invalidation address range with base address in Address >> [63:13]. If S field and >> Address[12] is Set and bit 13 is Clear, it indicates a 16KB invalidation >> address range with base >> address in Address [63:14], etc. >> >> " >> >> So if we receive an address whose [63] is 0 and the rest is all 1, it's then >> a [0, ~0ULL] invalidation. > Yes. I think invalidating the whole range is always fine. It's still not > arbitrary, right? E.g., we can't even invalidate (0x1000, 0x3000) with > device-iotlb because of the address mask, not to say sub-pages. Yes. > >> >>>>>> How about just convert to use a range [start, end] for any notifier and move >>>>>> the checks (e.g the assert) into the actual notifier implemented (vhost or >>>>>> vfio)? >>>>> IOMMUTLBEntry itself is the abstraction layer of TLB entry. Hardware TLB entry >>>>> is definitely not arbitrary range either (because AFAICT the hardware should >>>>> only cache PFN rather than address, so at least PAGE_SIZE aligned). >>>>> Introducing this flag will already make this trickier just to avoid introducing >>>>> another similar struct to IOMMUTLBEntry, but I really don't want to make it a >>>>> default option... Not to mention I probably have no reason to urge the rest >>>>> iommu notifier users (tcg, vfio) to change their existing good code to suite >>>>> any of the backend who can cooperate with arbitrary address ranges... >>>> Ok, so it looks like we need a dedicated notifiers to device IOTLB. >>> Or we can also make a new flag for device iotlb just like current UNMAP? Then >>> we replace the vhost type from UNMAP to DEVICE_IOTLB. But IMHO using the >>> ARBITRARY_LENGTH flag would work in a similar way. DEVICE_IOTLB flag could >>> also allow virtio/vhost to only receive one invalidation (now IIUC it'll >>> receive both iotlb and device-iotlb for unmapping a page when ats=on), but then >>> ats=on will be a must and it could break some old (misconfiged) qemu because >>> afaict previously virtio/vhost could even work with vIOMMU (accidentally) even >>> without ats=on. >> >> That's a bug and I don't think we need to workaround mis-configurated qemu >> :) > IMHO it depends on the strictness we want on the qemu cmdline API. :) > > We should at least check libvirt to make sure it's using ats=on always, then I > agree maybe we can avoid considering the rest... > > Thanks, Cc libvirt list, but I think we should fix libvirt if they don't provide "ats=on". Thanks