linux-kernel - Re: [PATCH hyperv-next v7 01/11] arm64: kvm, smccc: Introduce and use API for getting hypervisor UUID

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Message-ID: <86semjku7x.wl-maz@kernel.org>
Date: Tue, 08 Apr 2025 08:06:42 +0100
From: Marc Zyngier <maz@...nel.org>
To: Roman Kisel <romank@...ux.microsoft.com>
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Subject: Re: [PATCH hyperv-next v7 01/11] arm64: kvm, smccc: Introduce and use API for getting hypervisor UUID

On Mon, 07 Apr 2025 21:13:26 +0100,
Roman Kisel <romank@...ux.microsoft.com> wrote:
> 
> The KVM/arm64 uses SMCCC to detect hypervisor presence. That code is
> private, and it follows the SMCCC specification. Other existing and
> emerging hypervisor guest implementations can and should use that
> standard approach as well.
> 
> Factor out a common infrastructure that the guests can use, update KVM
> to employ the new API. The central notion of the SMCCC method is the
> UUID of the hypervisor, and the new API follows that.
> 
> No functional changes. Validated with a KVM/arm64 guest.
> 
> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
> ---
>  arch/arm64/kvm/hypercalls.c        | 10 +++--
>  drivers/firmware/smccc/kvm_guest.c | 10 +----
>  drivers/firmware/smccc/smccc.c     | 17 ++++++++
>  include/linux/arm-smccc.h          | 64 ++++++++++++++++++++++++++++--
>  4 files changed, 85 insertions(+), 16 deletions(-)
>

[...]

> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index 67f6fdf2e7cd..4bb38f0e3fe2 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -7,6 +7,11 @@
>  
>  #include <linux/args.h>
>  #include <linux/init.h>
> +
> +#ifndef __ASSEMBLER__
> +#include <linux/uuid.h>
> +#endif

That's a pretty unusual guard in arm64 land. Looking at the current
state of the kernel:

$ git grep -w __ASSEMBLER__ arch/arm64/ | wc -l
2
$ git grep -w __ASSEMBLY__ arch/arm64/ | wc -l
122

I'd suggest the later rather than the former.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.