linux-kernel - Re: [RFC PATCH 13/15] iommufd: Persist iommu domains for live update

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Message-ID: <20250929160034.GG2695987@ziepe.ca>
Date: Mon, 29 Sep 2025 13:00:34 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Samiullah Khawaja <skhawaja@...gle.com>
Cc: David Woodhouse <dwmw2@...radead.org>,
	Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>, iommu@...ts.linux.dev,
	YiFei Zhu <zhuyifei@...gle.com>,
	Robin Murphy <robin.murphy@....com>,
	Pratyush Yadav <pratyush@...nel.org>,
	Kevin Tian <kevin.tian@...el.com>, linux-kernel@...r.kernel.org,
	Saeed Mahameed <saeedm@...dia.com>,
	Adithya Jayachandran <ajayachandra@...dia.com>,
	Parav Pandit <parav@...dia.com>,
	Leon Romanovsky <leonro@...dia.com>, William Tu <witu@...dia.com>,
	Vipin Sharma <vipinsh@...gle.com>, dmatlack@...gle.com,
	Chris Li <chrisl@...nel.org>, praan@...gle.com
Subject: Re: [RFC PATCH 13/15] iommufd: Persist iommu domains for live update

On Sun, Sep 28, 2025 at 07:06:21PM +0000, Samiullah Khawaja wrote:
> +static int iommufd_save_ioas(struct iommufd_ctx *ictx,
> +			     struct iommufd_lu *iommufd_lu)
> +{
> +	struct iommufd_hwpt_paging *hwpt_paging;
> +	struct iommufd_ioas *ioas = NULL;
> +	struct iommufd_object *obj;
> +	unsigned long index;
> +	int rc;
> +
> +	/* Iterate each ioas. */
> +	xa_for_each(&ictx->objects, index, obj) {
> +		if (obj->type != IOMMUFD_OBJ_IOAS)
> +			continue;

Wrong locking

> +
> +		ioas = (struct iommufd_ioas *)obj;
> +		mutex_lock(&ioas->mutex);
> +
> +		/*
> +		 * TODO: Iterate over each device of this iommufd and only save
> +		 * hwpt/domain if the device is persisted.
> +		 */
> +		list_for_each_entry(hwpt_paging, &ioas->hwpt_list, hwpt_item) {
> +			if (!hwpt_paging->common.domain)
> +				continue;

I don't think this should be automatic. The user should directly
serialize/unserialize HWPTs by ID.

Jason