> -----Original Message----- > From: Jason Gunthorpe <jgg@xxxxxxxx> > Sent: Wednesday, March 5, 2025 12:58 PM > To: Wathsala Wathawana Vithanage <wathsala.vithanage@xxxxxxx> > Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>; linux- > kernel@xxxxxxxxxxxxxxx; nd <nd@xxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>; > Philipp Stanner <pstanner@xxxxxxxxxx>; Yunxiang Li <Yunxiang.Li@xxxxxxx>; > Dr. David Alan Gilbert <linux@xxxxxxxxxxx>; Ankit Agrawal <ankita@xxxxxxxxxx>; > open list:VFIO DRIVER <kvm@xxxxxxxxxxxxxxx>; Dhruv Tripathi > <Dhruv.Tripathi@xxxxxxx>; Honnappa Nagarahalli > <Honnappa.Nagarahalli@xxxxxxx>; Jeremy Linton <Jeremy.Linton@xxxxxxx> > Subject: Re: [RFC PATCH] vfio/pci: add PCIe TPH to device feature ioctl > > On Wed, Mar 05, 2025 at 06:11:22AM +0000, Wathsala Wathawana Vithanage > wrote: > > > By not enabling TPH in device-specific mode, hypervisors can ensure > > that setting an ST in a device-specific location (like queue contexts) > > will have no effect. VMs should also not be allowed to enable TPH. > > So many workloads run inside VMs now for security reasons that is not a > reasonable approach. > > > I believe this could > > be enforced by trapping (causing VM exits) on MSI-X/ST table writes. > > Yes, I think this was always part of the plan for virtualization when using a MSI-X > table. > > > Having said that, regardless of this proposal or the availability of > > kernel TPH support, a VFIO driver could enable TPH and set an > > arbitrary ST on the MSI-X/ST table or a device-specific location on > > supported platforms. If the driver doesn't have a list of valid STs, > > it can enumerate 8- or 16-bit STs and measure access latencies to determine > valid ones. > > And you think it is absolutely true that no TPH value can cause a platform > malfunction or security failure? > I think such hardware bugs are inevitable :). Would disabling TPH in the kernel and preventing config-writes that enables TPH from the user-space by trapping them in the kernel work as a solution? That requires trapping config-writes. --wathsala
