From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lu Baolu Subject: Re: [PATCH v2 0/7] iommu/vt-d: Fix-up device-domain relationship by refactoring to use iommu group default domain. Date: Wed, 20 Mar 2019 09:26:59 +0800 Message-ID: <418d1432-2036-3f6f-48de-77005807e350@linux.intel.com> References: <0F0C82BE-86E5-4BAC-938C-6F7629E18D27@arista.com> <83B82113-8AE5-4B0C-A079-F389520525BD@arista.com> <0e74cc54-bb90-a620-5763-466cb11aaef7@linux.intel.com> <94706334-3DE4-4964-8FDD-125C58D493A0@arista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <94706334-3DE4-4964-8FDD-125C58D493A0@arista.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: James Sewart Cc: baolu.lu@linux.intel.com, iommu@lists.linux-foundation.org, Tom Murphy , Dmitry Safonov , Jacob Pan , linux-kernel@vger.kernel.org List-Id: iommu@lists.linux-foundation.org Hi James, On 3/19/19 9:35 PM, James Sewart wrote: > Hey Lu, > >> On 15 Mar 2019, at 03:13, Lu Baolu wrote: >> >> Hi James, >> >> On 3/14/19 7:56 PM, James Sewart wrote: >>> Patches 1 and 2 are the same as v1. >>> v1-v2: >>> Refactored ISA direct mappings to be returned by iommu_get_resv_regions. >>> Integrated patch by Lu to defer turning on DMAR until iommu.c has mapped >>> reserved regions. >>> Integrated patches by Lu to remove more unused code in cleanup. >>> Lu: I didn't integrate your patch to set the default domain type as it >>> isn't directly related to the aim of this patchset. Instead patch 4 >> >> Without those patches, user experience will be affected and some devices >> will not work on Intel platforms anymore. >> >> For a long time, Intel IOMMU driver has its own logic to determine >> whether a device requires an identity domain. For example, when user >> specifies "iommu=pt" in kernel parameter, all device will be attached >> with the identity domain. Further more, some quirky devices require >> an identity domain to be used before enabling DMA remapping, otherwise, >> it will not work. This was done by adding quirk bits in Intel IOMMU >> driver. >> >> So from my point of view, one way is porting all those quirks and kernel >> parameters into IOMMU generic layer, or opening a door for vendor IOMMU >> driver to determine the default domain type by their own. I prefer the >> latter option since it will not impact any behaviors on other >> architectures. > > I see your point. I’m not confident that using the proposed door to set a > groups default domain has the desired behaviour. As discussed before the > default domain type will be set based on the desired type for only the > first device attached to a group. I think to change the default domain > type you would need a slightly different door that wasn’t conditioned on > device. I think this as another problem. Just a summarize for the ease of discussion. We saw two problems: 1. When allocating a new group for a device, how should we determine the type of the default domain? This is what my proposal patches trying to address. 2. If we need to put a device into an existing group which uses a different type of domain from what the device desires to use, we might break the functionality of the device. For this problem I'd second your proposal below if I get your point correctly. > > For situations where individual devices require an identity domain because > of quirks then maybe calling is_identity_map per device in > iommu_group_get_for_dev is a better solution than the one I proposed. > Do you mean if we see a quirky device requires a different domain type other than the default domain type of the group, we will assign a new group to it? That looks good to me as far as I can see. I suppose this should be done in vt-d's ops callback. Best regards, Lu Baolu