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Tsirkin" To: Andi Kleen Cc: Dan Williams , "Kuppuswamy, Sathyanarayanan" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Andy Lutomirski , Bjorn Helgaas , Richard Henderson , Thomas Bogendoerfer , James E J Bottomley , Helge Deller , "David S . Miller" , Arnd Bergmann , Jonathan Corbet , Peter H Anvin , Dave Hansen , Tony Luck , Kirill Shutemov , Sean Christopherson , Kuppuswamy Sathyanarayanan , X86 ML , Linux Kernel Mailing List , Linux PCI , linux-alpha@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch , Linux Doc Mailing List , virtualization@lists.linux-foundation.org Subject: Re: [PATCH v4 11/15] pci: Add pci_iomap_shared{,_range} Message-ID: <20210824053830-mutt-send-email-mst@kernel.org> References: <20210805005218.2912076-1-sathyanarayanan.kuppuswamy@linux.intel.com> <20210805005218.2912076-12-sathyanarayanan.kuppuswamy@linux.intel.com> <20210823195409-mutt-send-email-mst@kernel.org> <26a3cce5-ddf7-cbe6-a41e-58a2aea48f78@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Mon, Aug 23, 2021 at 07:14:18PM -0700, Andi Kleen wrote: > > On 8/23/2021 6:04 PM, Dan Williams wrote: > > On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan > > 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 > > > > > Signed-off-by: Kuppuswamy Sathyanarayanan > > > > 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. > > We originally made it default (similar to AMD), but it during code audit we > found a lot of drivers who do ioremap early outside the probe function. > Since it would be difficult to change them all we made it opt-in, which > ensures that only drivers that have been enabled can talk with the host at > all and can't be attacked. That made the problem of hardening all these > drivers a lot more practical. > > Currently we only really need virtio and MSI-X shared, so for changing two > places in the tree you avoid a lot of headache elsewhere. > > Note there is still a command line option to override if you want to allow > and load other drivers. > > -Andi I see. Hmm. It's a bit of a random thing to do it at the map time though. E.g. DMA is all handled transparently behind the DMA API. Hardening is much more than just replacing map with map_shared and I suspect what you will end up with is basically vendors replacing map with map shared to make things work for their users and washing their hands. I would say an explicit flag in the driver that says "hardened" and refusing to init a non hardened one would be better. -- MST