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Re: [RISC-V] Switch to H-mode
- To: "oleksii.kurochko@xxxxxxxxx" <oleksii.kurochko@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Alistair Francis <Alistair.Francis@xxxxxxx>
- Date: Mon, 23 Jan 2023 22:32:01 +0000
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- Cc: "bobbyeshleman@xxxxxxxxx" <bobbyeshleman@xxxxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>, "gianluca@xxxxxxxxxxxx" <gianluca@xxxxxxxxxxxx>, "andrew.cooper3@xxxxxxxxxx" <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Mon, 23 Jan 2023 22:32:32 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [RISC-V] Switch to H-mode
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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.
Alistair
>
> Thanks in advance.
>
> ~ Oleksii
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