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Wed, 1 Apr 2020 17:56:44 +0000 (UTC) Received: from w520.home (ovpn-112-162.phx2.redhat.com [10.3.112.162]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6B47A5C1C6; Wed, 1 Apr 2020 17:56:39 +0000 (UTC) Date: Wed, 1 Apr 2020 11:56:38 -0600 From: Alex Williamson To: Kirti Wankhede Subject: Re: [PATCH v17 Kernel 6/7] vfio iommu: Adds flag to indicate dirty pages tracking capability support Message-ID: <20200401115638.08a2b389@w520.home> In-Reply-To: <20200401115103.4e8f81d9@w520.home> References: <1585587044-2408-1-git-send-email-kwankhede@nvidia.com> <1585587044-2408-7-git-send-email-kwankhede@nvidia.com> <20200330145814.32d9b652@w520.home> <6c6e6625-6dfd-d885-23fe-511744816d5b@nvidia.com> <20200331131539.390259e1@w520.home> <20200401115103.4e8f81d9@w520.home> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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: Zhengxiao.zx@Alibaba-inc.com, kevin.tian@intel.com, yi.l.liu@intel.com, cjia@nvidia.com, kvm@vger.kernel.org, eskultet@redhat.com, ziye.yang@intel.com, qemu-devel@nongnu.org, cohuck@redhat.com, shuangtai.tst@alibaba-inc.com, dgilbert@redhat.com, zhi.a.wang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, aik@ozlabs.ru, eauger@redhat.com, felipe@nutanix.com, jonathan.davies@nutanix.com, yan.y.zhao@intel.com, changpeng.liu@intel.com, Ken.Xue@amd.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 1 Apr 2020 11:51:03 -0600 Alex Williamson wrote: > On Wed, 1 Apr 2020 22:55:57 +0530 > Kirti Wankhede wrote: > > > On 4/1/2020 12:45 AM, Alex Williamson wrote: > > > On Wed, 1 Apr 2020 00:38:49 +0530 > > > Kirti Wankhede wrote: > > > > > >> On 3/31/2020 2:28 AM, Alex Williamson wrote: > > >>> On Mon, 30 Mar 2020 22:20:43 +0530 > > >>> Kirti Wankhede wrote: > > >>> > > >>>> Flag VFIO_IOMMU_INFO_DIRTY_PGS in VFIO_IOMMU_GET_INFO indicates that driver > > >>>> support dirty pages tracking. > > >>>> > > >>>> Signed-off-by: Kirti Wankhede > > >>>> Reviewed-by: Neo Jia > > >>>> --- > > >>>> drivers/vfio/vfio_iommu_type1.c | 3 ++- > > >>>> include/uapi/linux/vfio.h | 5 +++-- > > >>>> 2 files changed, 5 insertions(+), 3 deletions(-) > > >>>> > > >>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c > > >>>> index 266550bd7307..9fe12b425976 100644 > > >>>> --- a/drivers/vfio/vfio_iommu_type1.c > > >>>> +++ b/drivers/vfio/vfio_iommu_type1.c > > >>>> @@ -2390,7 +2390,8 @@ static long vfio_iommu_type1_ioctl(void *iommu_data, > > >>>> info.cap_offset = 0; /* output, no-recopy necessary */ > > >>>> } > > >>>> > > >>>> - info.flags = VFIO_IOMMU_INFO_PGSIZES; > > >>>> + info.flags = VFIO_IOMMU_INFO_PGSIZES | > > >>>> + VFIO_IOMMU_INFO_DIRTY_PGS; > > >>>> > > >>>> info.iova_pgsizes = vfio_pgsize_bitmap(iommu); > > >>>> > > >>>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > > >>>> index e3cbf8b78623..0fe7c9a6f211 100644 > > >>>> --- a/include/uapi/linux/vfio.h > > >>>> +++ b/include/uapi/linux/vfio.h > > >>>> @@ -985,8 +985,9 @@ struct vfio_device_feature { > > >>>> struct vfio_iommu_type1_info { > > >>>> __u32 argsz; > > >>>> __u32 flags; > > >>>> -#define VFIO_IOMMU_INFO_PGSIZES (1 << 0) /* supported page sizes info */ > > >>>> -#define VFIO_IOMMU_INFO_CAPS (1 << 1) /* Info supports caps */ > > >>>> +#define VFIO_IOMMU_INFO_PGSIZES (1 << 0) /* supported page sizes info */ > > >>>> +#define VFIO_IOMMU_INFO_CAPS (1 << 1) /* Info supports caps */ > > >>>> +#define VFIO_IOMMU_INFO_DIRTY_PGS (1 << 2) /* supports dirty page tracking */ > > >>>> __u64 iova_pgsizes; /* Bitmap of supported page sizes */ > > >>>> __u32 cap_offset; /* Offset within info struct of first cap */ > > >>>> }; > > >>> > > >>> > > >>> As I just mentioned in my reply to Yan, I'm wondering if > > >>> VFIO_CHECK_EXTENSION would be a better way to expose this. The > > >>> difference is relatively trivial, but currently the only flag > > >>> set by VFIO_IOMMU_GET_INFO is to indicate the presence of a field in > > >>> the returned structure. I think this is largely true of other INFO > > >>> ioctls within vfio as well and we're already using the > > >>> VFIO_CHECK_EXTENSION ioctl to check supported IOMMU models, and IOMMU > > >>> cache coherency. We'd simply need to define a VFIO_DIRTY_PGS_IOMMU > > >>> value (9) and return 1 for that case. Then when we enable support for > > >>> dirt pages that can span multiple mappings, we can add a v2 extensions, > > >>> or "MULTI" variant of this extension, since it should be backwards > > >>> compatible. > > >>> > > >>> The v2/multi version will again require that the user provide a zero'd > > >>> bitmap, but I don't think that should be a problem as part of the > > >>> definition of that version (we won't know if the user is using v1 or > > >>> v2, but a v1 user should only retrieve bitmaps that exactly match > > >>> existing mappings, where all bits will be written). Thanks, > > >>> > > >>> Alex > > >>> > > >> > > >> I look at these two ioctls as : VFIO_CHECK_EXTENSION is used to get > > >> IOMMU type, while VFIO_IOMMU_GET_INFO is used to get properties of a > > >> particular IOMMU type, right? > > > > > > Not exclusively, see for example VFIO_DMA_CC_IOMMU, > > > > > >> Then I think VFIO_IOMMU_INFO_DIRTY_PGS should be part of > > >> VFIO_IOMMU_GET_INFO and when we add code for v2/multi, a flag should be > > >> added to VFIO_IOMMU_GET_INFO. > > > > > > Which burns through flags, which is a far more limited resource than > > > our 32bit extension address space, especially when we're already > > > planning for one or more extensions to this support. Thanks, > > > > > > > To use flag from VFIO_IOMMU_GET_INFO was your original suggestion, only > > 3 bits are used here as of now. > > Sorry, I'm not infallible. Perhaps I was short sighted and thought we > might only need one flag, perhaps I forgot about the check-extension > ioctl. Are there any technical reasons to keep it on the get-info > ioctl? As I'm trying to look ahead for how we're going to fill the > gaps of this initial implementation, it seems to me that what we're > exposing here is in line with what we've used check-extension for in > the past, and it offers us essentially unlimited extensions to burn > through, while we're clearly limited on the get-info flags. We do have > the precedent of the reset flag on the device_get_info ioctl, but I'm > largely under the impression that was a mistake and queuing up multiple > missing features in addition to the base flags feels like compounding > another mistake. Thanks, Another option rather than check-extension that would make sense to me would be to add a migration capability to the capability chain for the iommu-get-info ioctl. We could have our own set of migration related flags in that capability. Thanks, Alex