linux-kernel - RE: [PATCH v2 05/10] iommufd: Add replace support in iommufd_access_set

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Date:   Thu, 9 Feb 2023 03:13:08 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH v2 05/10] iommufd: Add replace support in
 iommufd_access_set_ioas()

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Wednesday, February 8, 2023 5:18 AM
> 
> Support an access->ioas replacement in iommufd_access_set_ioas(), which
> sets the access->ioas to NULL provisionally so that any further incoming
> iommufd_access_pin_pages() callback can be blocked.
> 
> Then, call access->ops->unmap() to clean up the entire iopt. To allow an
> iommufd_access_unpin_pages() callback to happen via this unmap() call,
> add an ioas_unpin pointer so the unpin routine won't be affected by the
> "access->ioas = NULL" trick above.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>

move patch10 before this one.

> ---
>  drivers/iommu/iommufd/device.c          | 16 ++++++++++++++--
>  drivers/iommu/iommufd/iommufd_private.h |  1 +
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/device.c
> b/drivers/iommu/iommufd/device.c
> index f4bd6f532a90..10ce47484ffa 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -509,11 +509,23 @@ int iommufd_access_set_ioas(struct
> iommufd_access *access, u32 ioas_id)
>  		iommufd_ref_to_users(obj);
>  	}
> 
> +	/*
> +	 * Set ioas to NULL to block any further iommufd_access_pin_pages().
> +	 * iommufd_access_unpin_pages() can continue using access-
> >ioas_unpin.
> +	 */
> +	access->ioas = NULL;
> +
>  	if (cur_ioas) {
> +		if (new_ioas) {
> +			mutex_unlock(&access->ioas_lock);
> +			access->ops->unmap(access->data, 0, ULONG_MAX);
> +			mutex_lock(&access->ioas_lock);
> +		}

why does above only apply to a valid new_ioas? this is the cleanup on
cur_ioas then required even when new_ioas=NULL.

Instead here the check should be "if (access->ops->unmap)". with
patch10 the cleanup is required only for driver which is allowed to
pin pages.