From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 6880A20348620 for ; Wed, 9 May 2018 08:47:28 -0700 (PDT) Subject: Re: [PATCH v4 04/14] PCI/P2PDMA: Clear ACS P2P flags for all devices behind switches References: <20180423233046.21476-1-logang@deltatee.com> <20180423233046.21476-5-logang@deltatee.com> <64C231F5-DE36-415F-B308-3A423B0BBACB@raithlin.com> <15433946-f7f5-f610-4e80-380fb59920e5@redhat.com> <3C9FB262-A93C-4C8F-B1E0-85C6D6F78BC2@raithlin.com> <20180508180157.7c7b393f@w520.home> From: Don Dutile Message-ID: Date: Wed, 9 May 2018 11:47:31 -0400 MIME-Version: 1.0 In-Reply-To: <20180508180157.7c7b393f@w520.home> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Alex Williamson Cc: Jens Axboe , Keith Busch , linux-nvdimm , linux-rdma , "linux-pci@vger.kernel.org" , Linux Kernel Mailing List , "linux-nvme@lists.infradead.org" , "linux-block@vger.kernel.org" , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jason Gunthorpe , =?UTF-8?Q?Christian_K=c3=b6nig?= , Benjamin Herrenschmidt , Bjorn Helgaas , Max Gurtovoy , Christoph Hellwig List-ID: On 05/08/2018 08:01 PM, Alex Williamson wrote: > On Tue, 8 May 2018 19:06:17 -0400 > Don Dutile wrote: >> On 05/08/2018 05:27 PM, Stephen Bates wrote: >>> As I understand it VMs need to know because VFIO passes IOMMU >>> grouping up into the VMs. So if a IOMMU grouping changes the VM's >>> view of its PCIe topology changes. I think we even have to be >>> cognizant of the fact the OS running on the VM may not even support >>> hot-plug of PCI devices. >> Alex: >> Really? IOMMU groups are created by the kernel, so don't know how >> they would be passed into the VMs, unless indirectly via PCI(e) >> layout. At best, twiddling w/ACS enablement (emulation) would cause >> VMs to see different IOMMU groups, but again, VMs are not the >> security point/level, the host/HV's are. > > Correct, the VM has no concept of the host's IOMMU groups, only the > hypervisor knows about the groups, but really only to the extent of > which device belongs to which group and whether the group is viable. > Any runtime change to grouping though would require DMA mapping > updates, which I don't see how we can reasonably do with drivers, > vfio-pci or native host drivers, bound to the affected devices. Thanks, > > Alex > A change in iommu groups would/could require a device remove/add cycle to get an updated DMA-mapping (yet-another-overused-term: iommu 'domain'). _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm