linux-kernel - Re: [RFC] iommu/virtio: Use single flush queue (EXPERIMENTAL)

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Message-ID: <ZMpduWLdRXhUEx6O@ziepe.ca>
Date:   Wed, 2 Aug 2023 10:44:25 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC] iommu/virtio: Use single flush queue (EXPERIMENTAL)

On Wed, Aug 02, 2023 at 01:36:12PM +0100, Jean-Philippe Brucker wrote:

> automatically get plugged into a VM without user intervention. Here I
> guess the devices we don't trust will be virtual devices implemented by
> other VMs. We don't have any method to identify them yet, so
> iommu.strict=1 and CONFIG_IOMMU_DEFAULT_DMA_STRICT is the best we can do
> at the moment.

VM's should work the same way as bare metal. The hypervisor should
pass in an ACPI/etc indication if specific devices are to be
untrusted. Otherwise the VM should assume trusted devices.

The hypervisor can already read all the VM's memory, it doesn't make
alot of sense for the VM to try and be defensive here in the general
case.

Jason