Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Alex Williamson <alex.williamson@redhat.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Robin Murphy <robin.murphy@arm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        David Gibson <david@gibson.dropbear.id.au>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Jason Wang <jasowang@redhat.com>
References: <20210603123401.GT1002214@nvidia.com>
 <20210603140146.5ce4f08a.alex.williamson@redhat.com>
 <20210603201018.GF1002214@nvidia.com>
 <20210603154407.6fe33880.alex.williamson@redhat.com>
 <MWHPR11MB1886469C0136C6523AB158B68C3B9@MWHPR11MB1886.namprd11.prod.outlook.com>
 <20210604122830.GK1002214@nvidia.com>
 <20210604092620.16aaf5db.alex.williamson@redhat.com>
 <815fd392-0870-f410-cbac-859070df1b83@redhat.com>
 <20210604155016.GR1002214@nvidia.com>
 <30e5c597-b31c-56de-c75e-950c91947d8f@redhat.com>
 <20210604160336.GA414156@nvidia.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal
Message-ID: <2c62b5c7-582a-c710-0436-4ac5e8fd8b39@redhat.com>
Date:   Fri, 4 Jun 2021 18:10:51 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.10.1
MIME-Version: 1.0
In-Reply-To: <20210604160336.GA414156@nvidia.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 04/06/21 18:03, Jason Gunthorpe wrote:
> On Fri, Jun 04, 2021 at 05:57:19PM +0200, Paolo Bonzini wrote:
>> I don't want a security proof myself; I want to trust VFIO to make the right
>> judgment and I'm happy to defer to it (via the KVM-VFIO device).
>>
>> Given how KVM is just a device driver inside Linux, VMs should be a slightly
>> more roundabout way to do stuff that is accessible to bare metal; not a way
>> to gain extra privilege.
> 
> Okay, fine, lets turn the question on its head then.
> 
> VFIO should provide a IOCTL VFIO_EXECUTE_WBINVD so that userspace VFIO
> application can make use of no-snoop optimizations. The ability of KVM
> to execute wbinvd should be tied to the ability of that IOCTL to run
> in a normal process context.
> 
> So, under what conditions do we want to allow VFIO to giave a process
> elevated access to the CPU:

Ok, I would definitely not want to tie it *only* to CAP_SYS_RAWIO (i.e. 
#2+#3 would be worse than what we have today), but IIUC the proposal 
(was it yours or Kevin's?) was to keep #2 and add #1 with an 
enable/disable ioctl, which then would be on VFIO and not on KVM.  I 
assumed Alex was more or less okay with it, given he included me in the 
discussion.

If later y'all switch to "it's always okay to issue the enable/disable 
ioctl", I guess the rationale would be documented in the commit message.

Paolo

>>>    1) User has access to a device that can issue no-snoop TLPS
>>>    2) User has access to an IOMMU that can not block no-snoop (today)
>>>    3) Require CAP_SYS_RAW_IO
>>>    4) Anyone
> 
> Jason
>