Re: [RISC-V] Switch to H-mode

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

On Mon, 2023-01-23 at 22:32 +0000, Alistair Francis wrote:
> On Mon, 2023-01-23 at 18:56 +0200, Oleksii wrote:
> > Hi Alistair and community,
> > 
> > I am working on RISC-V support upstream for Xen based on your and
> > Bobby
> > patches.
> > 
> > Adding the RISC-V support I realized that Xen is ran in S-mode.
> > Output
> > of OpenSBI:
> >     ...
> >     Domain0 Next Mode         : S-mode
> >     ...
> > So the first my question is shouldn't it be in H-mode?
> 
> There is no H-mode in RISC-V.
> 
> When the Hypervisor extension exists the standard S-mode
> automatically
> becomes HS-mode. The two names can be used interchangeably (although
> the spec calls it HS-mode).
> 
> In this way Linux (with or without KVM support) and Xen all boot in
> the
> same mode and can choose to use virtulisation if desired.
> 
> > 
> > If I am right than it looks like we have to do a patch to OpenSBI
> > to
> > add support of H-mode as it is not supported now:
> > [1]
> > https://github.com/riscv-software-src/opensbi/blob/master/lib/sbi/sbi_domain.c#L380
> > [2]
> > https://github.com/riscv-software-src/opensbi/blob/master/include/sbi/riscv_encoding.h#L110
> > Please correct me if I am wrong.
> > 
> > The other option I see is to switch to H-mode in U-boot as I
> > understand
> > the classical boot flow is:
> >     OpenSBI -> U-boot -> Xen -> Domain{0,...}
> > If it is at all possible since U-boot will be in S mode after
> > OpenSBI.
> 
> S-mode is where you want to be. That's what Xen should start in.
> 
Thanks for clarification.

~ Oleksii
> Alistair
> 
> > 
> > Thanks in advance.
> > 
> > ~ Oleksii
>