Re: [PATCH v6 0/9] hw/iommufd: IOMMUFD Dirty Tracking

[Joao Martins]

On 23/07/2024 09:35, Cédric Le Goater wrote:
> On 7/22/24 23:13, Joao Martins wrote:
>> This small series adds support for IOMMU dirty tracking support via the
>> IOMMUFD backend. The hardware capability is available on most recent x86
>> hardware (and these SMMUv3 in upcoming v6.11). The series is divided
>> organized as follows:
>>
>> * Patches 1 - 7: IOMMUFD backend support for dirty tracking;
>>
>> Introduce auto domains -- Patch 3 goes into more detail, but the gist is that
>> we will find and attach a device to a compatible IOMMU domain, or allocate a 
>> new
>> hardware pagetable *or* rely on kernel IOAS attach (for mdevs). Afterwards 
>> the
>> workflow is relatively simple:
>>
>> 1) Probe device and allow dirty tracking in the HWPT
>> 2) Toggling dirty tracking on/off
>> 3) Read-and-clear of Dirty IOVAs
>>
>> The heuristics selected for (1) were to always request the HWPT for
>> dirty tracking if supported, or rely on device dirty page tracking. This
>> is a little simplistic and we aren't necessarily utilizing IOMMU dirty
>> tracking even if we ask during hwpt allocation.
>>
>> The unmap case is deferred until further vIOMMU support with migration
>> is added[3] which will then introduce the usage of
>> IOMMU_HWPT_GET_DIRTY_BITMAP_NO_CLEAR in GET_DIRTY_BITMAP ioctl in the
>> dma unmap bitmap flow.
>>
>> * Patches 8 - 9: Don't block live migration where there's no VF dirty
>> tracker, considering that we have IOMMU dirty tracking.
>>
>> Comments and feedback appreciated (on patches 1, 5, 8, 9)
>>
>> Cheers,
>>      Joao
>>
>> P.S. Suggest v6.11-rc as hypervisor kernel as there's
>> some bugs fixed there with regards to IOMMU hugepage dirty tracking.
>>
>> Changes since v5[6]:
>> * Remove patches 1-4 as these were commited to vfio-next
>> * Add the Rb by Cedric and Zhenzhong (previously patches 7, 8, 10, 11)
>> * Introduce VFIODevice::iommu_dirty_tracking and use it on patch 5, 8
>> to store whether we can use IOMMU dirty tracking.
>>
>> Changes since v4[5]:
>> * Add various Reviewed-by in patches 2,3,4,6,8,11
>> * Change error messages to mention IOMMU (Zhenzhong)
>> * Better improve the checking of dirty page tracking in
>>    vfio_migration_realize() to detect per-device IOMMU instead of using
>>    container dirty_page_supported().
>> * Improve various commit messages (Eric)
>> * Extract the caps::hw_caps into its own patch as it was miosleading to
>> be hidden in another patch (new patch 7)
>> * Restructure patch 1 helper to be vfio_device_is_mdev() and use
>> vfio::mdev directly in rest of patches (Cedric)
>> * Improve error messages of set,query dirty tracking (Cedric)
>> * Add missing casts to uintptr and uint64_t* (Cedric)
>> * Add missing commens to struct doc from aw_bits removal (and hw_caps
>> addition) (Eric)
>> * Fix the detach flow in auto domains (Eric)
>> * Set hwpt to NULL on detach (Eric)
>> * Spurious line (Eric)
>>
>> Changes since v3[5]:
>> * Skip HostIOMMUDevice::realize for mdev, and introduce a helper to check if
>> the VFIO
>>    device is mdev. (Zhenzhong)
>> * Skip setting IOMMU device for mdev (Zhenzhong)
>> * Add Zhenzhong review tag in patch 3
>> * Utilize vbasedev::bcontainer::dirty_pages_supported instead of introducing
>>    a new HostIOMMUDevice capability and thus remove the cap patch from the
>> series (Zhenzhong)
>> * Move the HostIOMMUDevice::realize() to be part of VFIODevice initialization
>> in attach_device()
>> while skipping it all together for mdev. (Cedric)
>> * Due to the previous item, had to remove aw_bits because it depends on 
>> device
>> attach being
>> finished, instead defer it to when get_cap() gets called.
>> * Skip auto domains for mdev instead of purposedly erroring out (Zhenzhong)
>> * Pass errp in all cases, and instead just free the error in case of -EINVAL
>>    in most of all patches, and also pass Error* in
>> iommufd_backend_alloc_hwpt() amd
>>    set/query dirty. This is made better thanks in part to skipping auto
>> domains for mdev (Cedric)
>>
>> Changes since RFCv2[4]:
>> * Always allocate hwpt with IOMMU_HWPT_ALLOC_DIRTY_TRACKING even if
>> we end up not actually toggling dirty tracking. (Avihai)
>> * Fix error handling widely in auto domains logic and all patches (Avihai)
>> * Reuse iommufd_backend_get_device_info() for capabilities (Zhenzhong)
>> * New patches 1 and 2 taking into consideration previous comments.
>> * Store hwpt::flags to know if we have dirty tracking (Avihai)
>> * New patch 8, that allows to query dirty tracking support after
>> provisioning. This is a cleaner way to check IOMMU dirty tracking support
>> when vfio::migration is iniitalized, as opposed to RFCv2 via device caps.
>> device caps way is still used because at vfio attach we aren't yet with
>> a fully initialized migration state.
>> * Adopt error propagation in query,set dirty tracking
>> * Misc improvements overall broadly and Avihai
>> * Drop hugepages as it's a bit unrelated; I can pursue that patch
>> * separately. The main motivation is to provide a way to test
>> without hugepages similar to what vfio_type1_iommu.disable_hugepages=1
>> does.
>>
>> Changes since RFCv1[2]:
>> * Remove intel/amd dirty tracking emulation enabling
>> * Remove the dirtyrate improvement for VF/IOMMU dirty tracking
>> [Will pursue these two in separate series]
>> * Introduce auto domains support
>> * Enforce dirty tracking following the IOMMUFD UAPI for this
>> * Add support for toggling hugepages in IOMMUFD
>> * Auto enable support when VF supports migration to use IOMMU
>> when it doesn't have VF dirty tracking
>> * Add a parameter to toggle VF dirty tracking
>>
>> [0]
>> https://lore.kernel.org/qemu-devel/20240201072818.327930-1-zhenzhong.duan@intel.com/
>> [1]
>> https://lore.kernel.org/qemu-devel/20240201072818.327930-10-zhenzhong.duan@intel.com/
>> [2]
>> https://lore.kernel.org/qemu-devel/20220428211351.3897-1-joao.m.martins@oracle.com/
>> [3]
>> https://lore.kernel.org/qemu-devel/20230622214845.3980-1-joao.m.martins@oracle.com/
>> [4]
>> https://lore.kernel.org/qemu-devel/20240212135643.5858-1-joao.m.martins@oracle.com/
>> [5]
>> 20240708143420.16953-1-joao.m.martins@oracle.com/">https://lore.kernel.org/qemu-devel/20240708143420.16953-1-joao.m.martins@oracle.com/
>> [6]
>> 20240719120501.81279-1-joao.m.martins@oracle.com/">https://lore.kernel.org/qemu-devel/20240719120501.81279-1-joao.m.martins@oracle.com/
>>
>> Joao Martins (9):
>>    vfio/iommufd: Introduce auto domain creation
>>    vfio/{iommufd,container}: Remove caps::aw_bits
>>    vfio/iommufd: Add hw_caps field to HostIOMMUDeviceCaps
>>    vfio/{iommufd,container}: Invoke HostIOMMUDevice::realize() during
>>      attach_device()
>>    vfio/iommufd: Probe and request hwpt dirty tracking capability
>>    vfio/iommufd: Implement VFIOIOMMUClass::set_dirty_tracking support
>>    vfio/iommufd: Implement VFIOIOMMUClass::query_dirty_bitmap support
>>    vfio/migration: Don't block migration device dirty tracking is
>>      unsupported
>>    vfio/common: Allow disabling device dirty page tracking
>>
>>   include/hw/vfio/vfio-common.h      |  13 +++
>>   include/sysemu/host_iommu_device.h |   5 +-
>>   include/sysemu/iommufd.h           |  11 ++
>>   backends/iommufd.c                 |  85 ++++++++++++++-
>>   hw/vfio/common.c                   |  19 ++--
>>   hw/vfio/container.c                |   9 +-
>>   hw/vfio/helpers.c                  |  11 ++
>>   hw/vfio/iommufd.c                  | 170 ++++++++++++++++++++++++++++-
>>   hw/vfio/migration.c                |  12 +-
>>   hw/vfio/pci.c                      |   3 +
>>   backends/trace-events              |   3 +
>>   11 files changed, 318 insertions(+), 23 deletions(-)
> 
> Applied to vfio-next with the changes that were discussed this morning.
> Please check.
> 

I think the only thing missing is in the fourth patch to add the comment Eric
suggested (see below). Other than that, looks good to me.

diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
index 50ffa4b77090..abb6f1a4b4a8 100644
--- a/hw/vfio/iommufd.c
+++ b/hw/vfio/iommufd.c
@@ -488,6 +488,13 @@ static bool iommufd_cdev_attach(const char *name,
VFIODevice *vbasedev,

     space = vfio_get_address_space(as);

+    /*
+     * The HostIOMMUDevice data from legacy backend is static and doesn't need
+     * any information from the (type1-iommu) backend to be initialized. In
+     * contrast however, the IOMMUFD HostIOMMUDevice data requires the iommufd
+     * FD to be connected and having a devid to be able to successfully call
+     * iommufd_backend_get_device_info().
+     */
     if (!vfio_device_hiod_realize(vbasedev, errp)) {
         goto err_alloc_ioas;
     }