linux-kernel - Re: [PATCH v5 03/22] KVM: arm64: Support SDEI

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Date:   Thu, 24 Mar 2022 07:48:19 +0000
From:   Oliver Upton <oupton@...gle.com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, maz@...nel.org,
        linux-kernel@...r.kernel.org, eauger@...hat.com,
        shan.gavin@...il.com, Jonathan.Cameron@...wei.com,
        pbonzini@...hat.com, vkuznets@...hat.com, will@...nel.org
Subject: Re: [PATCH v5 03/22] KVM: arm64: Support SDEI_VERSION hypercall

On Thu, Mar 24, 2022 at 12:07:34PM +0800, Gavin Shan wrote:

[...]

> > > Yeah, I was sticky to the pattern of "KVM". However, I think it's good
> > > to reuse the existing one. Lets use ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2
> > > if you agree. Its first two characters are "VM" at least.
> > 
> > Sounds fine to me. The only other nit I'd say is we should define a
> > macro for it too, something like:
> > 
> >    #define KVM_SDEI_VENDOR	ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2
> > 
> 
> Agreed, and the macro will be put into arch/arm64/include/asm/kvm_sdei.h.
> arch/arm64/include/uapi/asm/kvm_sdei_state.h isn't the right place because
> the dependent macro ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2 isn't exposed by
> ABI.

The argument could definitely be made that our vendor ID should be
promoted to UAPI. Even though linux is the only known user of our
vendor-specific hypercalls, nothing is stopping other software from
using them. Beyond that, these values should really never change anyway.

It isn't a big deal if you add it to internal headers, either, as the
only known consumer will be the kernel.

--
Thanks,
Oliver