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

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Message-ID: <YjtLVqBbL0jyFFZy@google.com>
Date:   Wed, 23 Mar 2022 16:31:18 +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 Wed, Mar 23, 2022 at 08:46:40PM +0800, Gavin Shan wrote:
> Hi Oliver,
> 
> On 3/23/22 2:04 AM, Oliver Upton wrote:
> > On Tue, Mar 22, 2022 at 04:06:51PM +0800, Gavin Shan wrote:
> > > This supports SDEI_VERSION hypercall by returning v1.1, which is
> > > the specification version we're following. The vendor is set to
> > > 'KVM'.
> > > 
> > > Signed-off-by: Gavin Shan <gshan@...hat.com>
> > > ---
> > >   arch/arm64/kvm/sdei.c | 10 ++++++++++
> > >   1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/arch/arm64/kvm/sdei.c b/arch/arm64/kvm/sdei.c
> > > index 8a9b477b8977..5a3a64cd6e84 100644
> > > --- a/arch/arm64/kvm/sdei.c
> > > +++ b/arch/arm64/kvm/sdei.c
> > > @@ -118,6 +118,14 @@ static bool remove_all_vcpu_events(struct kvm_vcpu *vcpu,
> > >   	return pending;
> > >   }
> > > +static unsigned long hypercall_version(struct kvm_vcpu *vcpu)
> > > +{
> > > +	/* v1.1 and the vendor is KVM */
> > > +	return (1UL << SDEI_VERSION_MAJOR_SHIFT) |
> > > +	       (1UL << SDEI_VERSION_MINOR_SHIFT) |
> > > +	       0x4b564d;
> > 
> > It looks like the SDEI specification states that the vendor-defined
> > version number is 32 bits. Could we just use one of the
> > ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_{0,3} values instead?
> > 
> > ASCII 'KVM' is neat, but in reality guest software will just throw it in
> > a macro regardless. Might as well use one of the values we've already
> > trained it to use :-)
> > 
> > Also, it would appear that guest discovery of SDEI relies upon KVM
> > reporting a valid SDEI version. IMO, this patch should come at the very
> > end when KVM actually implements SDEI.
> > 
> 
> 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

--
Thanks,
Oliver