Re: [PATCH 1/2] KVM: arm64: CSSELR_EL1 max is 13

From: Andrew Jones <drjones@redhat.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, pbonzini@redhat.com
Subject: Re: [PATCH 1/2] KVM: arm64: CSSELR_EL1 max is 13
Date: Thu, 26 Nov 2020 15:36:35 +0100	[thread overview]
Message-ID: <20201126143635.hsp6l74fon62p47t@kamzik.brq.redhat.com> (raw)
In-Reply-To: <5106d82b42174b86dd62bc9637b2b6a4@kernel.org>

On Thu, Nov 26, 2020 at 02:34:05PM +0000, Marc Zyngier wrote:
> On 2020-11-26 14:32, Andrew Jones wrote:
> > On Thu, Nov 26, 2020 at 02:13:44PM +0000, Marc Zyngier wrote:
> > > On 2020-11-26 13:46, Andrew Jones wrote:
> > > > Not counting TnD, which KVM doesn't currently consider, CSSELR_EL1
> > > > can have a maximum value of 0b1101 (13), which corresponds to an
> > > > instruction cache at level 7. With CSSELR_MAX set to 12 we can
> > > > only select up to cache level 6. Change it to 14.
> > > >
> > > > Signed-off-by: Andrew Jones <drjones@redhat.com>
> > > > ---
> > > >  arch/arm64/kvm/sys_regs.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > > > index c1fac9836af1..ef453f7827fa 100644
> > > > --- a/arch/arm64/kvm/sys_regs.c
> > > > +++ b/arch/arm64/kvm/sys_regs.c
> > > > @@ -169,7 +169,7 @@ void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64
> > > > val, int reg)
> > > >  static u32 cache_levels;
> > > >
> > > >  /* CSSELR values; used to index KVM_REG_ARM_DEMUX_ID_CCSIDR */
> > > > -#define CSSELR_MAX 12
> > > > +#define CSSELR_MAX 14
> > > >
> > > >  /* Which cache CCSIDR represents depends on CSSELR value. */
> > > >  static u32 get_ccsidr(u32 csselr)
> > > 
> > > Huh, nice catch. Do we need a CC: stable tag for this?
> > > 
> > 
> > Hi Marc,
> > 
> > I wasn't thinking so, because I'm not expecting there to actually
> > be hardware with seven cache levels in the wild any time soon. You
> > have more knowledge about what's out there and coming, though, so
> > feel free CC stable if needed.
> 
> That's actually what I was wondering, whether you had seen that in the
> wild already. Since you haven't (and I'm not aware of such a monstrosity),
> I'll queue it for 5.11.
> 
> Do you want me to take the selftest stuff at the same time?
>

Yes, please :)

Thanks,
drew