linux-kernel - RE: [RFC PATCH] vfio/pci: add PCIe TPH to device feature ioctl

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Message-ID:
 <PAWPR08MB8909781BE207255E830DE1589FAC2@PAWPR08MB8909.eurprd08.prod.outlook.com>
Date: Tue, 1 Apr 2025 23:38:01 +0000
From: Wathsala Wathawana Vithanage <wathsala.vithanage@....com>
To: Jason Gunthorpe <jgg@...pe.ca>, "Tian, Kevin" <kevin.tian@...el.com>
CC: Alex Williamson <alex.williamson@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, nd
	<nd@....com>, Philipp Stanner <pstanner@...hat.com>, Yunxiang Li
	<Yunxiang.Li@....com>, "Dr. David Alan Gilbert" <linux@...blig.org>, Ankit
 Agrawal <ankita@...dia.com>, "open list:VFIO DRIVER" <kvm@...r.kernel.org>,
	Dhruv Tripathi <Dhruv.Tripathi@....com>, Honnappa Nagarahalli
	<Honnappa.Nagarahalli@....com>, Jeremy Linton <Jeremy.Linton@....com>
Subject: RE: [RFC PATCH] vfio/pci: add PCIe TPH to device feature ioctl



> -----Original Message-----
> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Tuesday, April 1, 2025 9:12 AM
> To: Tian, Kevin <kevin.tian@...el.com>
> Cc: Wathsala Wathawana Vithanage <wathsala.vithanage@....com>; Alex
> Williamson <alex.williamson@...hat.com>; linux-kernel@...r.kernel.org; nd
> <nd@....com>; Philipp Stanner <pstanner@...hat.com>; Yunxiang Li
> <Yunxiang.Li@....com>; Dr. David Alan Gilbert <linux@...blig.org>; Ankit
> Agrawal <ankita@...dia.com>; open list:VFIO DRIVER <kvm@...r.kernel.org>;
> Dhruv Tripathi <Dhruv.Tripathi@....com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@....com>; Jeremy Linton <Jeremy.Linton@....com>
> Subject: Re: [RFC PATCH] vfio/pci: add PCIe TPH to device feature ioctl
> 
> On Wed, Mar 12, 2025 at 07:53:17AM +0000, Tian, Kevin wrote:
> 
> > Probably we should not allow device-specific mode unless the user is
> > capable of CAP_SYS_RAWIO? It allows an user to pollute caches on CPUs
> > which its processes are not affined to, hence could easily break SLAs
> > which CSPs try to achieve...
> 
> I'm not sure this is within the threat model for VFIO though..
> 
> qemu or the operator needs to deal with this by not permiting such HW to go into
> a VM.
> 
> Really we can't block device specific mode anyhow because we can't even
> discover it on the kernel side..
> 

We cannot block users from writing a steering-tag to a device specific location, but
can we use a capability to prevent users from enabling device specific mode on the device?