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Fri, 24 Apr 2020 14:17:25 +0000 (UTC) Received: from [10.36.114.19] (ovpn-114-19.ams2.redhat.com [10.36.114.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6301560605; Fri, 24 Apr 2020 14:17:07 +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 , Alex Williamson 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> From: Auger Eric Message-ID: <72e3ea5c-c98c-3e02-26d1-b956ee81e30f@redhat.com> Date: Fri, 24 Apr 2020 16:17:04 +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 = 2020/04/24 03:54:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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" , "bharatb.linux@gmail.com" , "qemu-arm@nongnu.org" , "jean-philippe@linaro.org" , "linuc.decode@gmail.com" , "eric.auger.pro@gmail.com" , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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. Thanks Eric > > Thanks > -Bharat > >> >> Alex > >