On Fri, May 21, 2021 at 11:08:15AM -0700, Palmer Dabbelt wrote:

On Fri, 21 May 2021 10:47:51 PDT (-0700), Greg KH wrote:

quoted

On Fri, May 21, 2021 at 07:21:12PM +0200, Paolo Bonzini wrote:

quoted

On 21/05/21 19:13, Palmer Dabbelt wrote:

quoted

quoted

I don't view this code as being in a state where it can be
maintained, at least to the standards we generally set within the
kernel.  The ISA extension in question is still subject to change, it
says so right at the top of the H extension <https://github.com/riscv/riscv-isa-manual/blob/master/src/hypervisor.tex#L4>

  {\bf Warning! This draft specification may change before being
accepted as standard by the RISC-V Foundation.}

To give a complete picture, the last three relevant changes have been in
August 2019, November 2019 and May 2020.  It seems pretty frozen to me.

In any case, I think it's clear from the experience with Android that
the acceptance policy cannot succeed.  The only thing that such a policy
guarantees, is that vendors will use more out-of-tree code.  Keeping a
fully-developed feature out-of-tree for years is not how Linux is run.

quoted

I'm not sure where exactly the line for real hardware is, but for
something like this it would at least involve some chip that is
widely availiable and needs the H extension to be useful

Anup said that "quite a few people have already implemented RISC-V
H-extension in hardware as well and KVM RISC-V works on real HW as well".
Those people would benefit from having KVM in the Linus tree.

Great, but is this really true?  If so, what hardware has this?  I have
a new RISC-V device right here next to me, what would I need to do to
see if this is supported in it or not?

You can probe the misa register, it should have the H bit set if it supports
the H extension.

To let everyone know, based on our private chat we had off-list, no, the
device I have does not support this extension, so unless someone can
point me at real hardware, I don't think this code needs to be
considered for merging anywhere just yet.

thanks,

greg k-h