linux-kernel - Re: [PATCH v5 00/13] iommufd: Add vIOMMU infrastructure (Part-2: vDEVICE)

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Message-ID: <20241028141726.GQ6956@nvidia.com>
Date: Mon, 28 Oct 2024 11:17:26 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, "will@...nel.org" <will@...nel.org>,
	"joro@...tes.org" <joro@...tes.org>,
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Subject: Re: [PATCH v5 00/13] iommufd: Add vIOMMU infrastructure (Part-2:
 vDEVICE)

> > to
> > a Context Table. This virt_id helps IOMMU drivers to link the vID to a pID
> > of the device against the physical IOMMU instance. This is essential for a
> > vIOMMU-based invalidation, where the request contains a device's vID for a
> > device cache flush, e.g. ATC invalidation.
> 
> probably connect this to vCMDQ passthrough? otherwise for sw-based
> invalidation the userspace can always replace vID with pID before
> submitting the request.

You can't just do that, the ID in the invalidation command has to be
validated by the kernel.

At that point you may as well just use the vID instead of inventing a
new means to validate raw pIDs.

VT-D avoided this so far because it is pushing the invalidation
through the device object and the device object provides the ID
directly. No IDs in commands, no switching devices during a command
batch.

Jason