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

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Message-ID: <55e5f8d2-2b81-4883-a9ac-ad1a426c4222@linux.microsoft.com>
Date: Mon, 21 Jul 2025 10:20:54 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: Sudeep Holla <sudeep.holla@....com>,
 Jack Thomson <jackabt.amazon@...il.com>
Cc: mark.rutland@....com, lpieralisi@...nel.org, arnd@...db.de,
 wei.liu@...nel.org, mhklinux@...look.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 maz@...nel.org, 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



On 7/21/2025 9:15 AM, Sudeep Holla wrote:
> (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.

MUCH appreciated!! Apologies for that miss in testing of the older
kernels. I'll check on our side and will fix what needs fixing.

> 

-- 
Thank you,
Roman