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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Tue, 24 Aug 2021 14:59:41 -0700
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Subject: Re: [PATCH v4 11/15] pci: Add pci_iomap_shared{,_range}
To:     Rajat Jain <rajatja@google.com>
Cc:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
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        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        James E J Bottomley <James.Bottomley@hansenpartnership.com>,
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        Jonathan Corbet <corbet@lwn.net>,
        Peter H Anvin <hpa@zytor.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
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On Tue, Aug 24, 2021 at 2:57 PM Rajat Jain <rajatja@google.com> wrote:
>
> On Mon, Aug 23, 2021 at 6:06 PM Dan Williams <dan.j.williams@intel.com> wrote:
> >
> > On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan
> > <sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
> > >
> > >
> > >
> > > On 8/23/21 4:56 PM, Michael S. Tsirkin wrote:
> > > >> Add a new variant of pci_iomap for mapping all PCI resources
> > > >> of a devices as shared memory with a hypervisor in a confidential
> > > >> guest.
> > > >>
> > > >> Signed-off-by: Andi Kleen<ak@linux.intel.com>
> > > >> Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@linux.intel.com>
> > > > I'm a bit puzzled by this part. So why should the guest*not*  map
> > > > pci memory as shared? And if the answer is never (as it seems to be)
> > > > then why not just make regular pci_iomap DTRT?
> > >
> > > It is in the context of confidential guest (where VMM is un-trusted). So
> > > we don't want to make all PCI resource as shared. It should be allowed
> > > only for hardened drivers/devices.
> >
> > That's confusing, isn't device authorization what keeps unaudited
> > drivers from loading against untrusted devices? I'm feeling like
> > Michael that this should be a detail that drivers need not care about
> > explicitly, in which case it does not need to be exported because the
> > detail can be buried in lower levels.
> >
> > Note, I specifically said "unaudited", not "hardened" because as Greg
> > mentioned the kernel must trust drivers, its devices that may not be
> > trusted.
>
> Can you please point me to the thread where this discussion with Greg
> is ongoing?

It slowed down to implement the "move to the 'authorized' device
model" recommendation. LWN has a good writeup (as usual) and a link to
the thread:

https://lwn.net/Articles/865918/