On Tue, Aug 13, 2024 at 04:55:27PM +0100, Conor Dooley wrote: > On Mon, Aug 12, 2024 at 05:45:30PM -0700, Charlie Jenkins wrote: > > On Fri, Aug 09, 2024 at 11:31:15PM +0100, Conor Dooley wrote: > > > On Tue, Aug 06, 2024 at 05:31:36PM -0700, Charlie Jenkins wrote: > > > > xtheadvector is a custom extension that is based upon riscv vector > > > > version 0.7.1 [1]. All of the vector routines have been modified to > > > > support this alternative vector version based upon whether xtheadvector > > > > was determined to be supported at boot. > > > > > > > > vlenb is not supported on the existing xtheadvector hardware, so a > > > > devicetree property thead,vlenb is added to provide the vlenb to Linux. > > > > > > > > There is a new hwprobe key RISCV_HWPROBE_KEY_VENDOR_EXT_THEAD_0 that is > > > > used to request which thead vendor extensions are supported on the > > > > current platform. This allows future vendors to allocate hwprobe keys > > > > for their vendor. > > > > > > > > Support for xtheadvector is also added to the vector kselftests. > > > > > > So uh, since noone seems to have brought it up, in the light of the issues > > > with thead's vector implementation, (https://ghostwriteattack.com/) do we > > > want to enable it at all? > > > > I can make it clear in the kconfig that xtheadvector is succeptible to > > this attack and that it should be enabled with caution. I think we > > should let people that understand the risk to enable it. > > I think the clearest way might be "depends on BROKEN"? Sorry for the delay, I am not sure if BROKEN is the best way of doing this. There is the generic CPU_MITIGATIONS config that I think we should use to handle this at boot time. This would allow generic kernels to be used on the platform, but a kernel config of "mitigations=off" would allow xtheadvector to be enabled. I'll look into this a bit more and send out a patch. Palmer merged a patch into for-next to enable GENERIC_CPU_VULNERABILITIES for riscv so I will add ghostwrite there as well. - Charlie
