linux-kernel - Re: [PATCH] swiotlb: Validate bounce size in the sync/unmap path

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Message-ID: <20210203193638.GA325136@fedora>
Date:   Wed, 3 Feb 2021 14:36:38 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Martin Radev <martin.b.radev@...il.com>, m.szyprowski@...sung.com,
        robin.murphy@....com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, joro@...tes.org,
        kirill.shutemov@...ux.intel.com, thomas.lendacky@....com,
        robert.buhren@...t.tu-berlin.de, file@...t.tu-berlin.de,
        mathias.morbitzer@...ec.fraunhofer.de,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org
Subject: Re: [PATCH] swiotlb: Validate bounce size in the sync/unmap path

On Wed, Feb 03, 2021 at 01:49:22PM +0100, Christoph Hellwig wrote:
> On Mon, Jan 18, 2021 at 12:44:58PM +0100, Martin Radev wrote:
> > Your comment makes sense but then that would require the cooperation
> > of these vendors and the cloud providers to agree on something meaningful.
> > I am also not sure whether the end result would be better than hardening
> > this interface to catch corruption. There is already some validation in
> > unmap path anyway.
> 
> So what?  If you guys want to provide a new capability you'll have to do
> work.  And designing a new protocol based around the fact that the
> hardware/hypervisor is not trusted and a copy is always required makes
> a lot of more sense than throwing in band aids all over the place.

If you don't trust the hypervisor, what would this capability be in?

I suppose you mean this would need to be in the the guest kernel and
this protocol would depend on .. not-hypervisor and most certainly not
the virtio or any SR-IOV device. That removes a lot of options.

The one sensibile one (since folks will trust OEM vendors like Intel
or AMD to provide the memory encryption so they will also trust the
IOMMU - I hope?) - and they do have plans for that with their IOMMU
frameworks which will remove the need for SWIOTLB (I hope).

But that is not now, but in future.