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Tue, 31 Mar 2020 19:15:42 +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 64A0E5C1BB; Tue, 31 Mar 2020 19:15:40 +0000 (UTC) Date: Tue, 31 Mar 2020 13:15:39 -0600 From: Alex Williamson To: Kirti Wankhede Cc: , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v17 Kernel 6/7] vfio iommu: Adds flag to indicate dirty pages tracking capability support Message-ID: <20200331131539.390259e1@w520.home> In-Reply-To: <6c6e6625-6dfd-d885-23fe-511744816d5b@nvidia.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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, Alex