Re: [PATCH v3 04/19] iommufd: Add a flag to enforce dirty tracking on attach

Jason Gunthorpe
2023-10-13T15:52:17Z

On Sat, Sep 23, 2023 at 02:24:56AM +0100, Joao Martins wrote:
> Throughout IOMMU domain lifetime that wants to use dirty tracking, some
> guarantees are needed such that any device attached to the iommu_domain
> supports dirty tracking.
>
> The idea is to handle a case where IOMMU in the system are assymetric
> feature-wise and thus the capability may not be supported for all devices.
> The enforcement is done by adding a flag into HWPT_ALLOC namely:
>
> IOMMUFD_HWPT_ALLOC_ENFORCE_DIRTY
>
> .. Passed in HWPT_ALLOC ioctl() flags. The enforcement is done by creating
> a iommu_domain via domain_alloc_user() and validating the requested flags
> with what the device IOMMU supports (and failing accordingly) advertised).
> Advertising the new IOMMU domain feature flag requires that the individual
> iommu driver capability is supported when a future device attachment
> happens.
>
> Link: https://lore.kernel.org/kvm/20220721142421.GB4609@nvidia.com/
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
> drivers/iommu/iommufd/hw_pagetable.c | 8 ++++++--
> include/uapi/linux/iommufd.h | 3 +++
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> index 26a8a818ffa3..32e259245314 100644
> --- a/drivers/iommu/iommufd/hw_pagetable.c
> +++ b/drivers/iommu/iommufd/hw_pagetable.c
> @@ -83,7 +83,9 @@ iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
>
> lockdep_assert_held(&ioas->mutex);
>
> - if ((flags & IOMMU_HWPT_ALLOC_NEST_PARENT) && !ops->domain_alloc_user)
> + if ((flags & (IOMMU_HWPT_ALLOC_NEST_PARENT|
> + IOMMU_HWPT_ALLOC_ENFORCE_DIRTY)) &&
> + !ops->domain_alloc_user)
> return ERR_PTR(-EOPNOTSUPP);

This seems strange, why are we testing flags here? shouldn't this just
be

if (flags && !ops->domain_alloc_user)
return ERR_PTR(-EOPNOTSUPP);

?

> hwpt = iommufd_object_alloc(ictx, hwpt, IOMMUFD_OBJ_HW_PAGETABLE);
> @@ -157,7 +159,9 @@ int iommufd_hwpt_alloc(struct iommufd_ucmd *ucmd)
> struct iommufd_ioas *ioas;
> int rc;
>
> - if (cmd->flags & ~IOMMU_HWPT_ALLOC_NEST_PARENT || cmd->__reserved)
> + if ((cmd->flags &
> + ~(IOMMU_HWPT_ALLOC_NEST_PARENT|IOMMU_HWPT_ALLOC_ENFORCE_DIRTY)) ||
> + cmd->__reserved)
> return -EOPNOTSUPP;

Please checkpatch your stuff, and even better feed the patches to
clang-format and do most of what it says.

Otherwise seems like the right thing to do

Jason