linux-kernel - Re: [PATCH] arm64: kvm, smccc: Fix vendor uuid

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Message-ID: <20250721-proficient-carrot-cockatoo-393ae1@sudeepholla>
Date: Mon, 21 Jul 2025 17:15:46 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Jack Thomson <jackabt.amazon@...il.com>
Cc: mark.rutland@....com, lpieralisi@...nel.org, arnd@...db.de,
	wei.liu@...nel.org, romank@...ux.microsoft.com,
	mhklinux@...look.com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, maz@...nel.org,
	Sudeep Holla <sudeep.holla@....com>, oliver.upton@...ux.dev,
	kvmarm@...ts.linux.dev, roypat@...zon.com,
	Jack Thomson <jackabt@...zon.com>
Subject: Re: [PATCH] arm64: kvm, smccc: Fix vendor uuid

(I can't see this original patch in my mailbox, got only Marc's response)

On Mon, Jul 21, 2025 at 02:05:58PM +0100, Jack Thomson wrote:
> From: Jack Thomson <jackabt@...zon.com>
> 
> Commit 13423063c7cb ("arm64: kvm, smccc: Introduce and use API for
> getting hypervisor UUID") replaced the explicit register constants
> with the UUID_INIT macro. However, there is an endian issue, meaning
> the UUID generated and used in the handshake didn't match UUID prior to
> the commit.
> 
> The change in UUID causes the SMCCC vendor handshake to fail with older
> guest kernels, meaning devices such as PTP were not available in the
> guest.
> 
> This patch updates the parameters to the macro to generate a UUID which
> matches the previous value, and re-establish backwards compatibility
> with older guest kernels.
> 

Nice catch. This is result of classic confusion with UUID and GUID especially
coming from Microsoft who tend to use GUID more.

Reviewed-by: Sudeep Holla <sudeep.holla@....com>

This also makes me wonder if the initialisation in arch/arm64/hyperv/mshyperv.c
is also wrong or may be that's correct only MS guys can confirm as I couldn't
find the UUID string for that.

-- 
Regards,
Sudeep