[PATCH] arm64: kvm, smccc: Fix vendor uuid

[Will Deacon]

On Mon, Jul 21, 2025 at 04:59:36PM +0100, Marc Zyngier wrote:
> [+Will]
> 
> On Mon, 21 Jul 2025 14:05:58 +0100,
> Jack Thomson <jackabt.amazon at gmail.com> wrote:
> > 
> > From: Jack Thomson <jackabt at amazon.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.
> > 
> > Fixes: 13423063c7cb ("arm64: kvm, smccc: Introduce and use API for getting hypervisor UUID")
> > getting hypervisor UUID")
> > Signed-off-by: Jack Thomson <jackabt at amazon.com>
> > ---
> >  include/linux/arm-smccc.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> > index 784ebe4607a4..50b47eba7d01 100644
> > --- a/include/linux/arm-smccc.h
> > +++ b/include/linux/arm-smccc.h
> > @@ -113,7 +113,7 @@
> >  
> >  /* KVM UID value: 28b46fb6-2ec5-11e9-a9ca-4b564d003a74 */
> >  #define ARM_SMCCC_VENDOR_HYP_UID_KVM UUID_INIT(\
> > -	0xb66fb428, 0xc52e, 0xe911, \
> > +	0x28b46fb6, 0x2ec5, 0x11e9, \
> >  	0xa9, 0xca, 0x4b, 0x56, \
> >  	0x4d, 0x00, 0x3a, 0x74)
> >  
> > 
> 
> Irk. This is remarkably embarrassing, and needs to be addressed ASAP,
> before 6.16 ships. FWIW, I've just posted a quickly whipped selftest
> that shows the problem[1].
> 
> Will, is there a chance you can pick this up and ferry it to Linus?
> If you do, please add:
> 
> Reviewed-by: Marc Zyngier <maz at kernel.org>
> Tested-by: Marc Zyngier <maz at kernel.org>

Sure, I'll grab it. Thanks!

Will