Re: [PATCH v9 00/13] riscv: Add support for xtheadvector

Conor Dooley
2024-08-13T15:55:46Z

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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"?

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