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

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:

quoted

On Tue, Aug 06, 2024 at 05:31:36PM -0700, Charlie Jenkins wrote:

quoted

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"?