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: > > On Fri, May 21, 2021 at 07:21:12PM +0200, Paolo Bonzini wrote: > > > On 21/05/21 19:13, Palmer Dabbelt wrote: > > > > > > > > > > > > > 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. > > > > > > > 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
