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Tue, 5 May 2020 12:05:08 +0000 (UTC) Subject: Re: [EXT] Re: [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio region translation by viommu To: Bharat Bhushan References: <20200323084617.1782-1-bbhushan2@marvell.com> <20200323084617.1782-2-bbhushan2@marvell.com> <20200323170835.5021f845@w520.home> <8ec6af3c-6bd7-a3dc-c531-16db6b2089c5@redhat.com> <20200326115318.094ab79a@x1.home> <72e3ea5c-c98c-3e02-26d1-b956ee81e30f@redhat.com> <987c2781-ce4d-9c6a-eae6-ac53fdc581c0@redhat.com> From: Auger Eric Message-ID: <5a5f423b-88f0-1295-a107-025e5269fbc9@redhat.com> Date: Tue, 5 May 2020 14:05:07 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=eric.auger@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/05 03:48:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "yang.zhong@intel.com" , "peter.maydell@linaro.org" , "kevin.tian@intel.com" , "Tomasz Nowicki \[C\]" , "mst@redhat.com" , "drjones@redhat.com" , "peterx@redhat.com" , "qemu-devel@nongnu.org" , Alex Williamson , "qemu-arm@nongnu.org" , "jean-philippe@linaro.org" , Bharat Bhushan , David Gibson , "linuc.decode@gmail.com" , "eric.auger.pro@gmail.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Bharat, On 5/5/20 12:18 PM, Bharat Bhushan wrote: > Hi Eric, > > On Tue, May 5, 2020 at 3:16 PM Bharat Bhushan wrote: >> >> hi Eric, >> >> On Tue, May 5, 2020 at 3:00 PM Auger Eric wrote: >>> >>> Hi Bharat, >>> >>> On 5/5/20 11:25 AM, Bharat Bhushan wrote: >>>> Hi Eric, >>>> >>>> On Fri, Apr 24, 2020 at 7:47 PM Auger Eric wrote: >>>>> >>>>> Hi Bharat, >>>>> >>>>> On 4/2/20 11:01 AM, Bharat Bhushan wrote: >>>>>> Hi Eric/Alex, >>>>>> >>>>>>> -----Original Message----- >>>>>>> From: Alex Williamson >>>>>>> Sent: Thursday, March 26, 2020 11:23 PM >>>>>>> To: Auger Eric >>>>>>> Cc: Bharat Bhushan ; peter.maydell@linaro.org; >>>>>>> peterx@redhat.com; eric.auger.pro@gmail.com; kevin.tian@intel.com; >>>>>>> mst@redhat.com; Tomasz Nowicki [C] ; >>>>>>> drjones@redhat.com; linuc.decode@gmail.com; qemu-devel@nongnu.org; qemu- >>>>>>> arm@nongnu.org; bharatb.linux@gmail.com; jean-philippe@linaro.org; >>>>>>> yang.zhong@intel.com; David Gibson >>>>>>> Subject: [EXT] Re: [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio >>>>>>> region translation by viommu >>>>>>> >>>>>>> External Email >>>>>>> >>>>>>> ---------------------------------------------------------------------- >>>>>>> On Thu, 26 Mar 2020 18:35:48 +0100 >>>>>>> Auger Eric wrote: >>>>>>> >>>>>>>> Hi Alex, >>>>>>>> >>>>>>>> On 3/24/20 12:08 AM, Alex Williamson wrote: >>>>>>>>> [Cc +dwg who originated this warning] >>>>>>>>> >>>>>>>>> On Mon, 23 Mar 2020 14:16:09 +0530 >>>>>>>>> Bharat Bhushan wrote: >>>>>>>>> >>>>>>>>>> On ARM, the MSI doorbell is translated by the virtual IOMMU. >>>>>>>>>> As such address_space_translate() returns the MSI controller MMIO >>>>>>>>>> region and we get an "iommu map to non memory area" >>>>>>>>>> message. Let's remove this latter. >>>>>>>>>> >>>>>>>>>> Signed-off-by: Eric Auger >>>>>>>>>> Signed-off-by: Bharat Bhushan >>>>>>>>>> --- >>>>>>>>>> hw/vfio/common.c | 2 -- >>>>>>>>>> 1 file changed, 2 deletions(-) >>>>>>>>>> >>>>>>>>>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c index >>>>>>>>>> 5ca11488d6..c586edf47a 100644 >>>>>>>>>> --- a/hw/vfio/common.c >>>>>>>>>> +++ b/hw/vfio/common.c >>>>>>>>>> @@ -426,8 +426,6 @@ static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb, >>>>>>> void **vaddr, >>>>>>>>>> &xlat, &len, writable, >>>>>>>>>> MEMTXATTRS_UNSPECIFIED); >>>>>>>>>> if (!memory_region_is_ram(mr)) { >>>>>>>>>> - error_report("iommu map to non memory area %"HWADDR_PRIx"", >>>>>>>>>> - xlat); >>>>>>>>>> return false; >>>>>>>>>> } >>>>>>>>>> >>>>>>>>> >>>>>>>>> I'm a bit confused here, I think we need more justification beyond >>>>>>>>> "we hit this warning and we don't want to because it's ok in this >>>>>>>>> one special case, therefore remove it". I assume the special case >>>>>>>>> is that the device MSI address is managed via the SET_IRQS ioctl and >>>>>>>>> therefore we won't actually get DMAs to this range. >>>>>>>> Yes exactly. The guest creates a mapping between one giova and this >>>>>>>> gpa (corresponding to the MSI controller doorbell) because MSIs are >>>>>>>> mapped on ARM. But practically the physical device is programmed with >>>>>>>> an host chosen iova that maps onto the physical MSI controller's >>>>>>>> doorbell. so the device never performs DMA accesses to this range. >>>>>>>> >>>>>>>> But I imagine the case that >>>>>>>>> was in mind when adding this warning was general peer-to-peer >>>>>>>>> between and assigned and emulated device. >>>>>>>> yes makes sense. >>>>>>>> >>>>>>>> Maybe there's an argument to be made >>>>>>>>> that such a p2p mapping might also be used in a non-vIOMMU case. We >>>>>>>>> skip creating those mappings and drivers continue to work, maybe >>>>>>>>> because nobody attempts to do p2p DMA with the types of devices we >>>>>>>>> emulate, maybe because p2p DMA is not absolutely reliable on bare >>>>>>>>> metal and drivers test it before using it. >>>>>>>> MSI doorbells are mapped using the IOMMU_MMIO flag (dma-iommu.c >>>>>>>> iommu_dma_get_msi_page). >>>>>>>> One idea could be to pass that flag through the IOMMU Notifier >>>>>>>> mechanism into the iotlb->perm. Eventually when we get this in >>>>>>>> vfio_get_vaddr() we would not print the warning. Could that make sense? >>>>>>> >>>>>>> Yeah, if we can identify a valid case that doesn't need a warning, that's fine by me. >>>>>>> Thanks, >>>>>> >>>>>> Let me know if I understood the proposal correctly: >>>>>> >>>>>> virtio-iommu driver in guest will make map (VIRTIO_IOMMU_T_MAP) with VIRTIO_IOMMU_MAP_F_MMIO flag for MSI mapping. >>>>>> In qemu, virtio-iommu device will set a new defined flag (say IOMMU_MMIO) in iotlb->perm in memory_region_notify_iommu(). vfio_get_vaddr() will check same flag and will not print the warning.> >>>>>> Is above correct? >>>>> Yes that's what I had in mind. >>>> >>>> In that case virtio-iommu driver in guest should not make map >>>> (VIRTIO_IOMMU_T_MAP) call as it known nothing to be mapped. >>> sorry I don't catch what you meant. Please can you elaborate? >> >> What I understood of the proposal is: >> Linux: >> 1) MSI doorbells are mapped using the IOMMU_MMIO flag (dma-iommu.c >> iommu_dma_get_msi_page) >> 2) virtio-iommu driver in guest will make map (VIRTIO_IOMMU_T_MAP) >> with VIRTIO_IOMMU_MAP_F_MMIO flag for MSI mapping. >> >> GEMU: >> 3) virtio-iommu device - If VIRTIO_IOMMU_MAP_F_MMIO flag set then will >> set a new defined flag (say IOMMU_MMIO) in iotlb->perm in >> memory_region_notify_iommu() >> 4. vfio_get_vaddr() will check same flag and will not print the >> warning. Also vfio_iommu_map_notify() will not do anything. >> >> So, rather than going down to step 3 and 4, can we avoid maling map() >> calling in step-2 itself? > > ohh, We need to setup msi translation mapping, correct. The virtio-iommu driver is supposed to obey the map() operation argument and cascade this to the device. I don't see why it would filter this out. Now we should have means to declare the vITS GPA as an HW MSI reserved region and avoid calling the map(). I will try this out. Thanks Eric > > Thanks > -Bharat > >> >> Thanks >> -Bharat >> >>> >>> Thanks >>> >>> Eric >>>> >>>> Stay Safe >>>> >>>> Thanks >>>> -Bharat >>>> >>>>> >>>>> Thanks >>>>> >>>>> Eric >>>>>> >>>>>> Thanks >>>>>> -Bharat >>>>>> >>>>>>> >>>>>>> Alex >>>>>> >>>>>> >>>>> >>>> >>> >