linux-kernel - Re: [PATCH v3] iommufd/device: Enforce reserved IOVA also when attached to hwpt

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Message-ID: <20240827142612.GN3773488@nvidia.com>
Date: Tue, 27 Aug 2024 11:26:12 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, yi.l.liu@...el.com, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] iommufd/device: Enforce reserved IOVA also when
 attached to hwpt_nested

On Tue, Aug 06, 2024 at 05:34:46PM -0700, Nicolin Chen wrote:
> Currently, device reserved regions are only enforced when the device is
> attached to an hwpt_paging. In other words, if the device gets attached
> to an hwpt_nested directly, the parent hwpt_paging of the hwpt_nested's
> would not enforce those reserved IOVAs. This works for most of reserved
> region types, but not for IOMMU_RESV_SW_MSI, which is a unique software
> defined window, required by a nesting case too to setup an MSI doorbell
> on the parent stage-2 hwpt/domain.
> 
> Kevin pointed out that:
> 1) there is no usage using up closely the entire IOVA space yet,
> 2) guest may change the viommu mode to switch between nested
>    and paging then VMM has to take all devices' reserved regions
>    into consideration anyway, when composing the GPA space.
> Link: https://lore.kernel.org/all/BN9PR11MB5276497781C96415272E6FED8CB12@BN9PR11MB5276.namprd11.prod.outlook.com/
> 
> So it would be actually convenient for us to also enforce reserved IOVA
> onto the parent hwpt_paging, when attaching a device to an hwpt_nested.
> 
> Repurpose the existing attach/replace_paging helpers to attach device's
> reserved IOVAs exclusively.
> 
> Add a new find_hwpt_paging helper, which is only used by these reserved
> IOVA functions, to allow an IOMMUFD_OBJ_HWPT_NESTED hwpt to redirect to
> its parent hwpt_paging. Return a NULL in these two helpers for any new
> HWPT type in the future.
> 
> Suggested-by: Tian, Kevin <kevin.tian@...el.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
> 
> Changelog
> v3:
>  * Moved to_hwpt_paging logic back to the callers
>  * Added a new find_hwpt_paging for reserved iova callers
> v2:
>  https://lore.kernel.org/all/20240806050201.3717816-1-nicolinc@nvidia.com/
>  * Corrected the ioas comparisons for future hwpt type that returns
>    NULL by the to_hwpt_paging helper.
> v1:
>  https://lore.kernel.org/all/20240802053458.2754673-1-nicolinc@nvidia.com/
> 
>  drivers/iommu/iommufd/device.c          | 52 ++++++++++++-------------
>  drivers/iommu/iommufd/iommufd_private.h | 19 +++++++++
>  2 files changed, 45 insertions(+), 26 deletions(-)

Applied to iommufd for-next

Thanks,
Jason