linux-kernel - Re: [PATCH 0/2] vfio/type1/pci: IOMMU PFNMAP invalidation

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Message-ID: <20200515095415.3dd4d253@w520.home>
Date:   Fri, 15 May 2020 09:54:15 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, cohuck@...hat.com
Subject: Re: [PATCH 0/2] vfio/type1/pci: IOMMU PFNMAP invalidation

On Fri, 15 May 2020 11:22:51 -0400
Peter Xu <peterx@...hat.com> wrote:

> On Thu, May 14, 2020 at 04:55:17PM -0600, Alex Williamson wrote:
> > > I'm not if this makes sense, can't we arrange to directly trap the
> > > IOMMU failure and route it into qemu if that is what is desired?  
> > 
> > Can't guarantee it, some systems wire that directly into their
> > management processor so that they can "protect their users" regardless
> > of whether they want or need it.  Yay firmware first error handling,
> > *sigh*.  Thanks,  
> 
> Sorry to be slightly out of topic - Alex, does this mean the general approach
> of fault reporting from vfio to the userspace is not gonna work too?

AFAIK these platforms only generate a fatal fault on certain classes of
access which imply a potential for data loss, for example a DMA write to
an invalid PTE entry.  The actual IOMMU page faulting mechanism should
not be affected by this, or at least one would hope.  Thanks,

Alex