linux-kernel - Re: [RFC PATCH 08/15] iommu/vt-d: Implement live update preserve_iommu

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Message-ID: <20250929155723.GE2695987@ziepe.ca>
Date: Mon, 29 Sep 2025 12:57:23 -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,
	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,
	zhuyifei@...gle.com, Chris Li <chrisl@...nel.org>, praan@...gle.com
Subject: Re: [RFC PATCH 08/15] iommu/vt-d: Implement live update
 preserve_iommu_context

On Sun, Sep 28, 2025 at 07:06:16PM +0000, Samiullah Khawaja wrote:
> +static int unpreserve_iommu_context(struct intel_iommu *iommu, int end)
> +{
> +	struct context_entry *context;
> +	int i;
> +
> +	if (end < 0)
> +		end = ROOT_ENTRY_NR;
> +
> +	for (i = 0; i < end; i++) {
> +		context = iommu_context_addr(iommu, i, 0, 0);
> +		if (context)
> +			WARN_ON_ONCE(kho_unpreserve_folio(virt_to_folio(context)));

Wrong function. IIRC all of these allocations came from iommu-pages.c
and have struct page metadata.

iommu-pages needs to participate in restoring them and put back it's
struct page information.

>  static int preserve_iommu_state(struct intel_iommu *iommu,
>  				struct iommu_unit_ser *ser)
>  {
> -	pr_warn("Not implemented\n");
> -	return 0;
> +	int ret;
> +
> +	spin_lock(&iommu->lock);
> +	ret = preserve_iommu_context(iommu);
> +	if (ret)
> +		goto error;
> +
> +	ret = kho_preserve_folio(virt_to_folio(iommu->root_entry));
> +	if (ret) {
> +		unpreserve_iommu_context(iommu, -1);
> +		goto error;
> +	}
> +
> +	ser->phys_addr = iommu->reg_phys;
> +	ser->root_table = __pa(iommu->root_entry);
> +	atomic_set(&iommu->preserved, 1);

Why all these atomics??

Also most probably this should all be flowing through the core code as
I think the core code has to genericall prevent attach/detach/probe
from happing once serialization has started.

Jason