linux-kernel - RE: [PATCH v3 3/5] iommu: Add iommu_get_domain_for_dev

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <BN9PR11MB52769ACDFED7201CE282FE3C8C34A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Fri, 15 Aug 2025 08:55:28 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>, "robin.murphy@....com"
	<robin.murphy@....com>, "joro@...tes.org" <joro@...tes.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>, "jgg@...dia.com"
	<jgg@...dia.com>
CC: "will@...nel.org" <will@...nel.org>, "robin.clark@....qualcomm.com"
	<robin.clark@....qualcomm.com>, "yong.wu@...iatek.com"
	<yong.wu@...iatek.com>, "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
	"angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>, "thierry.reding@...il.com"
	<thierry.reding@...il.com>, "vdumpa@...dia.com" <vdumpa@...dia.com>,
	"jonathanh@...dia.com" <jonathanh@...dia.com>, "rafael@...nel.org"
	<rafael@...nel.org>, "lenb@...nel.org" <lenb@...nel.org>, "Liu, Yi L"
	<yi.l.liu@...el.com>, "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-arm-msm@...r.kernel.org"
	<linux-arm-msm@...r.kernel.org>, "linux-mediatek@...ts.infradead.org"
	<linux-mediatek@...ts.infradead.org>, "linux-tegra@...r.kernel.org"
	<linux-tegra@...r.kernel.org>, "linux-acpi@...r.kernel.org"
	<linux-acpi@...r.kernel.org>, "linux-pci@...r.kernel.org"
	<linux-pci@...r.kernel.org>, "patches@...ts.linux.dev"
	<patches@...ts.linux.dev>, "Jaroszynski, Piotr" <pjaroszynski@...dia.com>,
	"Sethi, Vikram" <vsethi@...dia.com>, "helgaas@...nel.org"
	<helgaas@...nel.org>, "etzhao1900@...il.com" <etzhao1900@...il.com>
Subject: RE: [PATCH v3 3/5] iommu: Add iommu_get_domain_for_dev_locked()
 helper

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Tuesday, August 12, 2025 6:59 AM
> 
> There is a need to attach a PCI device that's under a reset to temporally
> the blocked domain (i.e. detach it from its previously attached domain),
> and then to reattach it back to its previous domain (i.e. detach it from
> the blocked domain) after reset.
> 
> During the reset stage, there can be races from other attach/detachment.
> To solve this, a per-gdev reset flag will be introduced so that all the
> attach functions will bypass the driver-level attach_dev callbacks, but
> only update the group->domain pointer. The reset recovery procedure will
> attach directly to the cached pointer so things will be back to normal.
> 
> On the other hand, the iommu_get_domain_for_dev() API always returns the
> group->domain pointer, and several IOMMMU drivers call this API in their
> attach_dev callback functions to get the currently attached domain for a
> device, which will be broken for the recovery case mentioned above:
>  1. core asks the driver to attach dev from blocked to group->domain
>  2. driver attaches dev from group->domain to group->domain

the 2nd bullet implies that a driver may skip the operation by noting that
old domain is same as the new one?

> 
> So, iommu_get_domain_for_dev() should check the gdev flag and return the
> blocked domain if the flag is set. But the caller of this API could hold
> the group->mutex already or not, making it difficult to add the lock.
> 
> Introduce a new iommu_get_domain_for_dev_locked() helper to be used by
> those drivers in a context that is already under the protection of the
> group->mutex, e.g. those attach_dev callback functions. And roll out the
> new helper to all the existing IOMMU drivers.

iommu_get_domain_for_dev() is also called outside of attach_dev
callback functions, e.g. malidp_get_pgsize_bitmap(). and the returned
info according to the attached domain might be saved in static
structures, e.g.:

	ms->mmu_prefetch_pgsize = malidp_get_pgsize_bitmap(mp);

would that cause weird issues when blocking domain is returned
though one may not expect reset to happen at that point?

> +/* Caller can be any general/external function that isn't an IOMMU callback
> */
>  struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)

s/can/must/ ?