linux-kernel - Re: [PATCH v3 1/6] kvm: determine memory type from VMA

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Message-ID: <ZDarrZmLWlA+BHQG@nvidia.com>
Date:   Wed, 12 Apr 2023 10:01:33 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     ankita@...dia.com, alex.williamson@...hat.com,
        naoya.horiguchi@....com, oliver.upton@...ux.dev,
        aniketa@...dia.com, cjia@...dia.com, kwankhede@...dia.com,
        targupta@...dia.com, vsethi@...dia.com, acurrid@...dia.com,
        apopple@...dia.com, jhubbard@...dia.com, danw@...dia.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 1/6] kvm: determine memory type from VMA

On Wed, Apr 12, 2023 at 01:43:26PM +0100, Marc Zyngier wrote:

> What makes it safe? How does VFIO ensures that the memory type used is
> correct in all circumstances? This has to hold for *ANY* device, not
> just your favourite toy of the day. Nothing in this patch is horribly
> wrong, but the above question must be answered before we can consider
> any of this.

In VFIO we now have the concept of "variant drivers" which work with
specific PCI IDs. The variant drivers can inject device specific
knowledge into VFIO. In this series the driver injects the cachable
pgprot when it creates some of the VMAs because it knows the PCI IDs
it supports, parses the ACPI description, and knows for sure that the
memory it puts in the cachable VMA is linked with a cache coherent
interconnect.

The generic vfio-pci path is not changed, so 'any device' is not
relevant here.

Jason